curl in php version 7.3 post data are empty in endpoint

i have trouble to solve problem for post-ing data from webpage to endpoint.
I create webpage in html/css and javascript. User can add or delete data and if user want to submit data, i use php to send this usercreated data with php to endpoint. Endpoint is database, where rest api is used. For the problem of CORS we added proxy server as nginx, which just listen to ip and port and redict from this incoming ip port to another ip and port. We added also SSL Cert from trusted CA. Sofar OK, but randomly post data comes empty to endpoint. Authenfitication for user sudmiting data happens over Bearer Token. All logs show valid bearer token and data “should” be there, but is empty on endpoint. I am really desperate for solution.
For security we also add cloudflare recaptca on client-site. I forget to mention, we dont own webserver. This host webprovider. I cant set any php.ini values.

We tried with different browser, ms edge, chrome, firefox, opera, result is always the same.