diff --git a/modules/ppcp-api-client/src/Authentication/UserIdToken.php b/modules/ppcp-api-client/src/Authentication/UserIdToken.php
index 19965d5c4..080091266 100644
--- a/modules/ppcp-api-client/src/Authentication/UserIdToken.php
+++ b/modules/ppcp-api-client/src/Authentication/UserIdToken.php
@@ -82,7 +82,7 @@ class UserIdToken {
 	 * @throws RuntimeException If something unexpected happens.
 	 */
 	public function id_token( string $target_customer_id = '' ): string {
-		$session_customer_id = WC()->session->get_customer_id() ?? '';
+		$session_customer_id = WC()->session->get_customer_id() ?: '';
 		if ( $session_customer_id && $this->cache->has( self::CACHE_KEY . (string) $session_customer_id ) ) {
 			return $this->cache->get( self::CACHE_KEY . (string) $session_customer_id );
 		}