diff --git a/server/middleware/error_handler.go b/server/middleware/error_handler.go
index 446a23d..8b28368 100644
--- a/server/middleware/error_handler.go
+++ b/server/middleware/error_handler.go
@@ -66,6 +66,7 @@ func ErrorHandler(c fiber.Ctx) error {
 					})
 				}
 			}
+			log.Error("Internal Server Error: ", err)
 			return c.Status(fiber.StatusInternalServerError).JSON(model.Response[any]{
 				Success: false,
 				Data:    nil,
diff --git a/server/service/collection.go b/server/service/collection.go
index 2674948..8380e77 100644
--- a/server/service/collection.go
+++ b/server/service/collection.go
@@ -1,7 +1,6 @@
 package service
 
 import (
-	"errors"
 	"nysoure/server/dao"
 	"nysoure/server/model"
 )
@@ -9,7 +8,7 @@ import (
 // Create a new collection.
 func CreateCollection(uid uint, title, article string, host string) (*model.CollectionView, error) {
 	if uid == 0 || title == "" || article == "" {
-		return nil, errors.New("invalid parameters")
+		return nil, model.NewRequestError("invalid parameters")
 	}
 	c, err := dao.CreateCollection(uid, title, article, findImagesInContent(article, host))
 	if err != nil {
@@ -22,14 +21,14 @@ func CreateCollection(uid uint, title, article string, host string) (*model.Coll
 // Update an existing collection with user validation.
 func UpdateCollection(uid, id uint, title, article string, host string) error {
 	if uid == 0 || id == 0 || title == "" || article == "" {
-		return errors.New("invalid parameters")
+		return model.NewRequestError("invalid parameters")
 	}
 	collection, err := dao.GetCollectionByID(id)
 	if err != nil {
 		return err
 	}
 	if collection.UserID != uid {
-		return errors.New("user does not have permission to update this collection")
+		return model.NewUnAuthorizedError("user does not have permission to update this collection")
 	}
 	return dao.UpdateCollection(id, title, article, findImagesInContent(article, host))
 }
@@ -47,7 +46,7 @@ func DeleteCollection(uint, id uint) error {
 	}
 
 	if user.ID != collection.UserID && !user.IsAdmin {
-		return errors.New("user does not have permission to delete this collection")
+		return model.NewUnAuthorizedError("user does not have permission to delete this collection")
 	}
 
 	return dao.DeleteCollection(id)
@@ -56,14 +55,14 @@ func DeleteCollection(uint, id uint) error {
 // Add a resource to a collection with user validation.
 func AddResourceToCollection(uid, collectionID, resourceID uint) error {
 	if uid == 0 || collectionID == 0 || resourceID == 0 {
-		return errors.New("invalid parameters")
+		return model.NewRequestError("invalid parameters")
 	}
 	collection, err := dao.GetCollectionByID(collectionID)
 	if err != nil {
 		return err
 	}
 	if collection.UserID != uid {
-		return errors.New("user does not have permission to modify this collection")
+		return model.NewUnAuthorizedError("user does not have permission to modify this collection")
 	}
 	return dao.AddResourceToCollection(collectionID, resourceID)
 }
@@ -71,14 +70,14 @@ func AddResourceToCollection(uid, collectionID, resourceID uint) error {
 // Remove a resource from a collection with user validation.
 func RemoveResourceFromCollection(uid, collectionID, resourceID uint) error {
 	if uid == 0 || collectionID == 0 || resourceID == 0 {
-		return errors.New("invalid parameters")
+		return model.NewRequestError("invalid parameters")
 	}
 	collection, err := dao.GetCollectionByID(collectionID)
 	if err != nil {
 		return err
 	}
 	if collection.UserID != uid {
-		return errors.New("user does not have permission to modify this collection")
+		return model.NewUnAuthorizedError("user does not have permission to modify this collection")
 	}
 	return dao.RemoveResourceFromCollection(collectionID, resourceID)
 }
@@ -86,7 +85,7 @@ func RemoveResourceFromCollection(uid, collectionID, resourceID uint) error {
 // Get a collection by ID.
 func GetCollectionByID(id uint) (*model.CollectionView, error) {
 	if id == 0 {
-		return nil, errors.New("invalid collection id")
+		return nil, model.NewRequestError("invalid collection id")
 	}
 	c, err := dao.GetCollectionByID(id)
 	if err != nil {
@@ -98,7 +97,7 @@ func GetCollectionByID(id uint) (*model.CollectionView, error) {
 // List collections of a user with pagination.
 func ListUserCollections(username string, page int) ([]*model.CollectionView, int64, error) {
 	if username == "" || page < 1 {
-		return nil, 0, errors.New("invalid parameters")
+		return nil, 0, model.NewRequestError("invalid parameters")
 	}
 	user, err := dao.GetUserByUsername(username)
 	if err != nil {
@@ -119,7 +118,7 @@ func ListUserCollections(username string, page int) ([]*model.CollectionView, in
 // List resources in a collection with pagination.
 func ListCollectionResources(collectionID uint, page int) ([]*model.ResourceView, int64, error) {
 	if collectionID == 0 || page < 1 {
-		return nil, 0, errors.New("invalid parameters")
+		return nil, 0, model.NewRequestError("invalid parameters")
 	}
 	resources, total, err := dao.ListCollectionResources(collectionID, page, pageSize)
 	if err != nil {
@@ -137,7 +136,7 @@ func ListCollectionResources(collectionID uint, page int) ([]*model.ResourceView
 // excludedRID: if >0, only return collections not containing this resource.
 func SearchUserCollections(username string, keyword string, excludedRID uint) ([]*model.CollectionView, error) {
 	if username == "" {
-		return nil, errors.New("invalid parameters")
+		return nil, model.NewRequestError("invalid parameters")
 	}
 	user, err := dao.GetUserByUsername(username)
 	if err != nil {