I have this array:
$list_desings_ids = array(\'hc1wXBL7zCsdfMu\',\'dhdsfHddfD\',\'otheridshere\');
With a die() + var_dumo() this array return
Your array not have key . try this
foreach($general_list_designs as $key_design=>$design) { #$desing->desing_id return me for example: hc1wXBL7zCsdfMu if(in_array($design->design_id, $list_desings_ids)) $final_designs[] = $design; }