Nextcloud acesso externo, não abre arquivos do onlyoffice

Guys,
I have an Ubuntu 20.04 Server, I installed NC 18.04 by snap.
In the local network I can open files in the onlyoffice normally, but in my external network I do not open any files that need onlyoffice.
onlyoffice external error

I also can’t change the NC to access via HTTPS, I read on some topics that onlyoffice only works on HTTPS.

Please help me, the NC locally is great, I need to leave it the same way externally.