I'm having the HTTP Error 504.0 error in my application.
Architecture.
I mounted a REST API using Slim on the server X (on the web). When I make any request
to this API from my computer the API returns me the data almost instantly. That is, it works correctly.
However, when I try to interact with the API through a PHP
application via AJAX
that I also mounted, being hosted on another server from another domain the error happens.