diff --git a/internal/api/handler/auth.go b/internal/api/handler/auth.go
index c4c5a5f..af924fb 100644
--- a/internal/api/handler/auth.go
+++ b/internal/api/handler/auth.go
@@ -89,6 +89,7 @@ func (h *AuthHandler) Refresh(w http.ResponseWriter, r *http.Request) {
 // @Tags Authorization
 // @Accept json
 // @Produce json
+// @Param payload body request.LogoutPayload true "Logout payload"
 // @Success 200 {object} nil
 // @Error 400 {object} response.ErrorResponse "failed to decode request body"
 // @Error 500 {object} response.ErrorResponse "failed to logout"
diff --git a/internal/api/handler/user.go b/internal/api/handler/user.go
index 0db4a6e..1e40b66 100644
--- a/internal/api/handler/user.go
+++ b/internal/api/handler/user.go
@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"log/slog"
 	"net/http"
 
@@ -29,6 +30,8 @@ func NewUserHandler(userService *domain.UserService, authService *domain.AuthSer
 // @Param payload body request.CreateUserPayload true "Create user payload"
 // @Success 201 {object} domain.User
 // @Error 400 {object} response.ErrorResponse "failed to decode request body"
+// @Error 400 {object} response.ErrorResponse "invite is expired"
+// @Error 409 {object} response.ErrorResponse "invite is already consumed"
 // @Error 400 {object} response.ErrorResponse "invite is invalid"
 // @Error 500 {object} response.ErrorResponse "failed to create user"
 // @Router /users [post]
@@ -47,7 +50,16 @@ func (h *UserHandler) CreateUser(w http.ResponseWriter, r *http.Request) {
 		slog.ErrorContext(ctx, "failed to register user",
 			slog.Any("error", err),
 			slog.Any("payload", payload))
-		response.Error(ctx, w, http.StatusInternalServerError, "failed to register")
+
+		if errors.Is(err, domain.ErrInviteExpired) {
+			response.Error(ctx, w, http.StatusBadRequest, "invite is expired")
+		} else if errors.Is(err, domain.ErrInviteConsumed) {
+			response.Error(ctx, w, http.StatusConflict, "invite is already consumed")
+		} else if errors.Is(err, domain.ErrInviteInvalid) {
+			response.Error(ctx, w, http.StatusBadRequest, "invite is invalid")
+		} else {
+			response.Error(ctx, w, http.StatusInternalServerError, "failed to register")
+		}
 		return
 	}
 
diff --git a/internal/api/router/router.go b/internal/api/router/router.go
index e027ab9..0296f3e 100644
--- a/internal/api/router/router.go
+++ b/internal/api/router/router.go
@@ -38,7 +38,7 @@ func NewMux(cfg Config) http.Handler {
 	apiMux.HandleFunc("POST /login", authHandler.Login)
 	apiMux.HandleFunc("POST /login/refresh", authHandler.Refresh)
 	apiMux.HandleFunc("POST /logout", authHandler.Logout)
-	apiMux.HandleFunc("POST /logout/all", authHandler.LogoutAllDevices)
+	apiMux.HandleFunc("POST /logout/all", protected(authHandler.LogoutAllDevices))
 
 	// Users
 	apiMux.HandleFunc("POST /users", userHandler.CreateUser)
diff --git a/internal/domain/invite.go b/internal/domain/invite.go
index c70119c..1ffb8ed 100644
--- a/internal/domain/invite.go
+++ b/internal/domain/invite.go
@@ -9,6 +9,7 @@ import (
 var (
 	ErrInviteIDMissing = errors.New("invite id is required")
 	ErrCodeMissing     = errors.New("invite code is required")
+	ErrInviteInvalid   = errors.New("invite is invalid")
 	ErrInviteExpired   = errors.New("invite is expired")
 	ErrInviteConsumed  = errors.New("invite is already consumed")
 )
diff --git a/internal/domain/registration.go b/internal/domain/registration.go
index b136e93..678f9da 100644
--- a/internal/domain/registration.go
+++ b/internal/domain/registration.go
@@ -3,6 +3,7 @@ package domain
 import (
 	"context"
 	"log/slog"
+	"time"
 )
 
 type RegistrationService struct {
@@ -22,6 +23,13 @@ func (s *RegistrationService) Register(ctx context.Context, inviteCode string, e
 		return nil, err
 	}
 
+	if invite.ConsumedAt != nil {
+		return nil, ErrInviteConsumed
+	}
+	if invite.ExpiresAt.Before(time.Now()) {
+		return nil, ErrInviteExpired
+	}
+
 	var user *User
 	err = s.tx.WithinTx(ctx, func(ctx context.Context) error {
 		user, err = s.UserService.CreateUser(ctx, email, username, password)
diff --git a/internal/repository/invite.go b/internal/repository/invite.go
index d19d26e..6932ed9 100644
--- a/internal/repository/invite.go
+++ b/internal/repository/invite.go
@@ -33,13 +33,22 @@ func (r *InviteRepo) CreateInvite(ctx context.Context, inviterUserID string, cod
 }
 
 func (r *InviteRepo) DeleteInvite(ctx context.Context, userID string, inviteID string) error {
-	_, err := r.conn(ctx).ExecContext(ctx,
+	res, err := r.conn(ctx).ExecContext(ctx,
 		"DELETE FROM invites WHERE id = $1 AND inviter_user_id = $2 AND consumed_at IS NULL",
 		inviteID, userID,
 	)
 	if err != nil {
 		return fmt.Errorf("failed to delete invite: %w", err)
 	}
+	affected, err := res.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("could not get rows affected: %w", err)
+	}
+	if affected < 1 {
+		// It's more of an assumption,
+		// but unless I encounter this being wrong, I'll keep it.
+		return domain.ErrInviteConsumed
+	}
 
 	return nil
 }
@@ -57,7 +66,7 @@ func (r *InviteRepo) ConsumeInvite(ctx context.Context, inviteID string, invitee
 		return fmt.Errorf("could not get rows affected: %w", err)
 	}
 	if affected < 1 {
-		return fmt.Errorf("invite not found or expired")
+		return domain.ErrInviteInvalid
 	}
 
 	return nil