diff --git a/packages/gin/challenge-3-validation-errors/submissions/22-7-co/solution.go b/packages/gin/challenge-3-validation-errors/submissions/22-7-co/solution.go
new file mode 100644
index 00000000..52c74067
--- /dev/null
+++ b/packages/gin/challenge-3-validation-errors/submissions/22-7-co/solution.go
@@ -0,0 +1,527 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+// Product represents a product in the catalog
+type Product struct {
+	ID          int                    `json:"id"`
+	SKU         string                 `json:"sku" binding:"required"`
+	Name        string                 `json:"name" binding:"required,min=3,max=100"`
+	Description string                 `json:"description" binding:"max=1000"`
+	Price       float64                `json:"price" binding:"required,min=0.01"`
+	Currency    string                 `json:"currency" binding:"required"`
+	Category    Category               `json:"category" binding:"required"`
+	Tags        []string               `json:"tags"`
+	Attributes  map[string]interface{} `json:"attributes"`
+	Images      []Image                `json:"images"`
+	Inventory   Inventory              `json:"inventory" binding:"required"`
+	CreatedAt   time.Time              `json:"created_at"`
+	UpdatedAt   time.Time              `json:"updated_at"`
+}
+
+// Category represents a product category
+type Category struct {
+	ID       int    `json:"id" binding:"required,min=1"`
+	Name     string `json:"name" binding:"required"`
+	Slug     string `json:"slug" binding:"required"`
+	ParentID *int   `json:"parent_id,omitempty"`
+}
+
+// Image represents a product image
+type Image struct {
+	URL       string `json:"url" binding:"required,url"`
+	Alt       string `json:"alt" binding:"required,min=5,max=200"`
+	Width     int    `json:"width" binding:"min=100"`
+	Height    int    `json:"height" binding:"min=100"`
+	Size      int64  `json:"size"`
+	IsPrimary bool   `json:"is_primary"`
+}
+
+// Inventory represents product inventory information
+type Inventory struct {
+	Quantity    int       `json:"quantity" binding:"required,min=0"`
+	Reserved    int       `json:"reserved" binding:"min=0"`
+	Available   int       `json:"available"` // Calculated field
+	Location    string    `json:"location" binding:"required"`
+	LastUpdated time.Time `json:"last_updated"`
+}
+
+// ValidationError represents a validation error
+type ValidationError struct {
+	Field   string      `json:"field"`
+	Value   interface{} `json:"value"`
+	Tag     string      `json:"tag"`
+	Message string      `json:"message"`
+	Param   string      `json:"param,omitempty"`
+}
+
+// APIResponse represents the standard API response format
+type APIResponse struct {
+	Success   bool              `json:"success"`
+	Data      interface{}       `json:"data,omitempty"`
+	Message   string            `json:"message,omitempty"`
+	Errors    []ValidationError `json:"errors,omitempty"`
+	ErrorCode string            `json:"error_code,omitempty"`
+	RequestID string            `json:"request_id,omitempty"`
+}
+
+// Global data stores (in a real app, these would be databases)
+var products = []Product{}
+var categories = []Category{
+	{ID: 1, Name: "Electronics", Slug: "electronics"},
+	{ID: 2, Name: "Clothing", Slug: "clothing"},
+	{ID: 3, Name: "Books", Slug: "books"},
+	{ID: 4, Name: "Home & Garden", Slug: "home-garden"},
+}
+var validCurrencies = []string{"USD", "EUR", "GBP", "JPY", "CAD", "AUD"}
+var validWarehouses = []string{"WH001", "WH002", "WH003", "WH004", "WH005"}
+var nextProductID = 1
+
+// TODO: Implement SKU format validator
+// SKU format: ABC-123-XYZ (3 letters, 3 numbers, 3 letters)
+func isValidSKU(sku string) bool {
+	// TODO: Implement SKU validation
+	// The SKU should match the pattern: ^[A-Z]{3}-\d{3}-[A-Z]{3}$
+	const skuRegPattern = `^[A-Z]{3}-\d{3}-[A-Z]{3}$`
+	var skuReg = regexp.MustCompile(skuRegPattern)
+	if skuReg.MatchString(sku) {
+		return true
+	}
+	return false
+}
+
+// TODO: Implement currency validator
+func isValidCurrency(currency string) bool {
+	// TODO: Check if the currency is in the validCurrencies slice
+	if currency == "" {
+		return false
+	}
+	for _, validCurrency := range validCurrencies {
+		if currency == validCurrency {
+			return true
+		}
+	}
+	return false
+}
+
+// TODO: Implement category validator
+func isValidCategory(categoryName string) bool {
+	// TODO: Check if the category name exists in the categories slice
+	if categoryName == "" {
+		return false
+	}
+	for _, category := range categories {
+		if category.Name == categoryName {
+			return true
+		}
+	}
+	return false
+}
+
+// TODO: Implement slug format validator
+func isValidSlug(slug string) bool {
+	// TODO: Implement slug validation
+	// Slug should match: ^[a-z0-9]+(?:-[a-z0-9]+)*$
+	const slugRegPattern = `^[a-z0-9]+(?:-[a-z0-9]+)*$`
+	var slugReg = regexp.MustCompile(slugRegPattern)
+	if slugReg.MatchString(slug) {
+		return true
+	}
+	return false
+}
+
+// TODO: Implement warehouse code validator
+func isValidWarehouseCode(code string) bool {
+	// TODO: Check if warehouse code is in validWarehouses slice
+	// Format should be WH### (e.g., WH001, WH002)
+	for _, warehouseCode := range validWarehouses {
+		if warehouseCode == code {
+			return true
+		}
+	}
+	return false
+}
+
+// TODO: Implement comprehensive product validation
+func validateProduct(product *Product) []ValidationError {
+	var errors []ValidationError
+
+	// TODO: Add custom validation logic:
+	// - Validate SKU format and uniqueness
+	if !isValidSKU(product.SKU) {
+		errors = append(errors, ValidationError{
+			Field:   "SKU",
+			Message: fmt.Sprintf("SKU %s is not valid", product.SKU),
+		})
+	} else {
+		for _, existing := range products {
+			if product.SKU == existing.SKU {
+				errors = append(errors, ValidationError{
+					Field:   "SKU",
+					Message: fmt.Sprintf("SKU %s is not valid", product.SKU),
+				})
+				break
+			}
+		}
+	}
+	// - Validate currency code
+	if !isValidCurrency(product.Currency) {
+		errors = append(errors, ValidationError{
+			Field:   "Currency",
+			Message: fmt.Sprintf("Currency %s is not valid", product.Currency),
+		})
+	}
+	// - Validate category exists
+	if !isValidCategory(product.Category.Name) {
+		errors = append(errors, ValidationError{
+			Field:   "Category",
+			Message: fmt.Sprintf("Category %s is not valid", product.Category.Name),
+		})
+	}
+	// - Validate slug format
+	if !isValidSlug(product.Category.Slug) {
+		errors = append(errors, ValidationError{
+			Field:   "Category",
+			Message: fmt.Sprintf("Category %s is not valid", product.Category.Name),
+		})
+	}
+	// - Validate warehouse code
+	if !isValidWarehouseCode(product.Inventory.Location) {
+		errors = append(errors, ValidationError{
+			Field:   "Inventory",
+			Message: fmt.Sprintf("Inventory %s is not valid", product.Inventory.Location),
+		})
+	}
+	// - Cross-field validations (reserved <= quantity, etc.)
+	if product.Inventory.Reserved > product.Inventory.Quantity {
+		errors = append(errors, ValidationError{
+			Field:   "Inventory",
+			Message: fmt.Sprintf("Inventory %s is not valid", product.Inventory.Location),
+		})
+	}
+	return errors
+}
+
+// TODO: Implement input sanitization
+func sanitizeProduct(product *Product) {
+	// TODO: Sanitize input data:
+	// - Trim whitespace from strings
+	product.SKU = strings.TrimSpace(product.SKU)
+	product.Name = strings.TrimSpace(product.Name)
+	product.Currency = strings.TrimSpace(product.Currency)
+	product.Description = strings.TrimSpace(product.Description)
+	product.Category.Name = strings.TrimSpace(product.Category.Name)
+	product.Category.Slug = strings.TrimSpace(product.Category.Slug)
+	for k, v := range product.Attributes {
+		if s, ok := v.(string); ok {
+			product.Attributes[k] = strings.TrimSpace(s)
+		}
+	}
+	// - Convert SKU to uppercase
+	product.SKU = strings.ToUpper(product.SKU)
+	// - Convert currency to uppercase
+	product.Currency = strings.ToUpper(product.Currency)
+	// - Convert slug to lowercase
+	product.Category.Slug = strings.ToLower(product.Category.Slug)
+	// - Calculate available inventory (quantity - reserved)
+	product.Inventory.Available = product.Inventory.Quantity - product.Inventory.Reserved
+	// - Set timestamps
+	now := time.Now()
+	product.Inventory.LastUpdated = now
+	product.Inventory.Available = product.Inventory.Quantity - product.Inventory.Reserved
+	if product.CreatedAt.IsZero() {
+		product.CreatedAt = now
+	}
+	product.UpdatedAt = now
+}
+
+// POST /products - Create single product
+func createProduct(c *gin.Context) {
+	var product Product
+
+	// TODO: Bind JSON and handle basic validation errors
+	if err := c.ShouldBindJSON(&product); err != nil {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Invalid JSON or basic validation failed",
+			Errors: []ValidationError{
+				ValidationError{Tag: "bind",
+					Message: "Invalid JSON or basic validation failed"},
+			}, // TODO: Convert gin validation errors
+		})
+		return
+	}
+
+	// TODO: Apply custom validation
+	validationErrors := validateProduct(&product)
+	if len(validationErrors) > 0 {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Validation failed",
+			Errors:  validationErrors,
+		})
+		return
+	}
+
+	// TODO: Sanitize input data
+	sanitizeProduct(&product)
+
+	// TODO: Set ID and add to products slice
+	product.ID = nextProductID
+	nextProductID++
+	products = append(products, product)
+
+	c.JSON(201, APIResponse{
+		Success: true,
+		Data:    product,
+		Message: "Product created successfully",
+	})
+}
+
+// POST /products/bulk - Create multiple products
+func createProductsBulk(c *gin.Context) {
+	var inputProducts []Product
+
+	if err := c.ShouldBindJSON(&inputProducts); err != nil {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Invalid JSON format",
+		})
+		return
+	}
+
+	// TODO: Implement bulk validation
+	type BulkResult struct {
+		Index   int               `json:"index"`
+		Success bool              `json:"success"`
+		Product *Product          `json:"product,omitempty"`
+		Errors  []ValidationError `json:"errors,omitempty"`
+	}
+
+	var results []BulkResult
+	var successCount int
+
+	// TODO: Process each product and populate results
+	for i, product := range inputProducts {
+		validationErrors := validateProduct(&product)
+		if len(validationErrors) > 0 {
+			results = append(results, BulkResult{
+				Index:   i,
+				Success: false,
+				Errors:  validationErrors,
+			})
+		} else {
+			sanitizeProduct(&product)
+			product.ID = nextProductID
+			nextProductID++
+			products = append(products, product)
+
+			results = append(results, BulkResult{
+				Index:   i,
+				Success: true,
+				Product: &product,
+			})
+			successCount++
+		}
+	}
+
+	c.JSON(200, APIResponse{
+		Success: successCount == len(inputProducts),
+		Data: map[string]interface{}{
+			"results":    results,
+			"total":      len(inputProducts),
+			"successful": successCount,
+			"failed":     len(inputProducts) - successCount,
+		},
+		Message: "Bulk operation completed",
+	})
+}
+
+// POST /categories - Create category
+func createCategory(c *gin.Context) {
+	var category Category
+
+	if err := c.ShouldBindJSON(&category); err != nil {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Invalid JSON or validation failed",
+		})
+		return
+	}
+
+	// TODO: Add category-specific validation
+	// - Validate slug format
+	if !isValidSlug(category.Slug) {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Invalid Slug",
+		})
+		return
+	}
+	// - Check parent category exists if specified
+
+	if category.ParentID != nil {
+		ok := false
+		for _, existing := range categories {
+			if existing.ID == *category.ParentID {
+				ok = true
+				break
+			}
+		}
+		if !ok {
+			c.JSON(400, APIResponse{
+				Success: false,
+				Message: "ParentCategory not found",
+			})
+			return
+		}
+	}
+
+	// - Ensure category name is unique
+	for _, existing := range categories {
+		if existing.Name == category.Name {
+			c.JSON(400, APIResponse{
+				Success: false,
+				Message: "Category already exists",
+			})
+			return
+		}
+	}
+	categories = append(categories, category)
+
+	c.JSON(201, APIResponse{
+		Success: true,
+		Data:    category,
+		Message: "Category created successfully",
+	})
+}
+
+// POST /validate/sku - Validate SKU format and uniqueness
+func validateSKUEndpoint(c *gin.Context) {
+	var request struct {
+		SKU string `json:"sku" binding:"required"`
+	}
+
+	if err := c.ShouldBindJSON(&request); err != nil {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "SKU is required",
+		})
+		return
+	}
+
+	// TODO: Implement SKU validation endpoint
+	// - Check format using isValidSKU
+	if !isValidSKU(request.SKU) {
+		c.JSON(200, APIResponse{
+			Success: false,
+			Message: "Invalid SKU",
+		})
+		return
+	}
+	// - Check uniqueness against existing products
+	for _, existing := range products {
+		if existing.SKU == request.SKU {
+			c.JSON(200, APIResponse{
+				Success: false,
+				Message: "SKU already exists",
+			})
+			return
+		}
+	}
+
+	c.JSON(200, APIResponse{
+		Success: true,
+		Message: "SKU is valid",
+	})
+}
+
+// POST /validate/product - Validate product without saving
+func validateProductEndpoint(c *gin.Context) {
+	var product Product
+
+	if err := c.ShouldBindJSON(&product); err != nil {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Invalid JSON format",
+		})
+		return
+	}
+
+	validationErrors := validateProduct(&product)
+	if len(validationErrors) > 0 {
+		c.JSON(400, APIResponse{
+			Success: false,
+			Message: "Validation failed",
+			Errors:  validationErrors,
+		})
+		return
+	}
+
+	c.JSON(200, APIResponse{
+		Success: true,
+		Message: "Product data is valid",
+	})
+}
+
+// GET /validation/rules - Get validation rules
+func getValidationRules(c *gin.Context) {
+	rules := map[string]interface{}{
+		"sku": map[string]interface{}{
+			"format":   "ABC-123-XYZ",
+			"required": true,
+			"unique":   true,
+		},
+		"name": map[string]interface{}{
+			"required": true,
+			"min":      3,
+			"max":      100,
+		},
+		"currency": map[string]interface{}{
+			"required": true,
+			"valid":    validCurrencies,
+		},
+		"warehouse": map[string]interface{}{
+			"format": "WH###",
+			"valid":  validWarehouses,
+		},
+		// TODO: Add more validation rules
+	}
+
+	c.JSON(200, APIResponse{
+		Success: true,
+		Data:    rules,
+		Message: "Validation rules retrieved",
+	})
+}
+
+// Setup router
+func setupRouter() *gin.Engine {
+	router := gin.Default()
+
+	// Product routes
+	router.POST("/products", createProduct)
+	router.POST("/products/bulk", createProductsBulk)
+
+	// Category routes
+	router.POST("/categories", createCategory)
+
+	// Validation routes
+	router.POST("/validate/sku", validateSKUEndpoint)
+	router.POST("/validate/product", validateProductEndpoint)
+	router.GET("/validation/rules", getValidationRules)
+
+	return router
+}
+
+func main() {
+	router := setupRouter()
+	router.Run(":8080")
+}