Frontend using async calls same way as sync to load json config which contains backend api url. To make calls to backend API and sometimes file is not loaded before they call Api. This results to calling on current domain instead on domain from json file. Moreover, blaming that be is returning incorrect response.

next step: replace json-payload with json-files over sftp...

This post gives me a weird feeling where I'm proud that I know exactly what you're talking about... but I'm also deeply ashamed that I know exactly what you're talking about.

Like, IDK man, maybe we should have just stopped at fopen and curl... or if not there at fs and request...

I don't know where the line was, I just know we've passed it.