php - 503 error on live environment ONLY when loading a laravel filemanager -

i getting 503 errors when loading guillermomartinez/filemanager-laravel.

this url browser trying load;

[my-web-root]filemanager/connectors?path=%2ffilemanager%2fuserfiles%2f&mode=getfolder&showthumbs=true&time=108 503 

the symptom loading screen never finish loading:

i must mention on local lamp server working without problems