Video stream problem in http server output behind the Box

My problem :

Context :

Box Bbox Fit Fiber 400 Mb/s firmware 20.8.8

NGINX/RTMP/HLS web server (Ubuntu connected directly to the Box in RJ 45) video powered by OBS Studio (Windows 11) connected to the Ubuntu server via Wi-Fi by ASUS router/VPN Nordnet.

Internally everything works well the http page is displayed and we can launch the video normally

OK on 127.0.0.1

Ok on Localhost

OK on the Fixed IP address of the Web server connected by cable to the Box

OK on the real external address of the Box and not on the address seen from the VPN (knowing that port 80 points to the IP address of the Web server)

OK on the domain name which returns to the external address of the Box (certainly via the Loopback of the Box) which suggests that all the parameters are correct

Externally (another local network or 4G connection) the web page is displayed but the video stream cannot be launched (video player timeout with message "the media could not be loaded, either because the server or network failed or because the format is not supported" ) just as if the Box (or a Bouygues server) or my NGINX/RTMP/HLS configuration does not allow the video stream to pass to the outside.

All possible tests have been made: deactivation of the firewall, Web server in DMZ, activation or deactivation of remote access to the box, etc, etc...

nothing helps the video stream stubbornly refuses to go out....

It works perfectly in the LAN, how to make it work perfectly in the WAN as well? can be an NGINX setting or etc/hosts file or NAT rule.....

Bouygues support does not even understand the problem and is unable to tell me if this is a characteristic of the Box or the chosen subscription or if other Box models would be more appropriate or with what parameters to play.

Please help me

thanks in advance