diff --git a/modules/ppcp-api-client/src/Repository/CustomerRepository.php b/modules/ppcp-api-client/src/Repository/CustomerRepository.php
index 9f21a2959..d703851ef 100644
--- a/modules/ppcp-api-client/src/Repository/CustomerRepository.php
+++ b/modules/ppcp-api-client/src/Repository/CustomerRepository.php
@@ -31,7 +31,7 @@ class CustomerRepository {
 	}
 
 	/**
-	 * Returns a unique ID for the given user ID.
+	 * Returns the customer ID for the given user ID.
 	 *
 	 * @param int $user_id The user ID.
 	 * @return string
@@ -39,9 +39,9 @@ class CustomerRepository {
 	public function customer_id_for_user( int $user_id ): string {
 		$guest_customer_id = get_user_meta( $user_id, 'ppcp_guest_customer_id', true );
 		if ( $guest_customer_id ) {
-			return $this->prefix .  $guest_customer_id;
+			return $this->prefix . $guest_customer_id;
 		}
 
-		return $this->prefix . $user_id;
+		return $this->prefix . (string) $user_id;
 	}
 }