I deployed Peertube via Docker but did not use the included nginx docker container and instead put Peertube behind an Apache httpd reverse proxy.
I was getting the error :
Cannot retrieve OAuth Client credentials: undefined when loading the peertube page
and the error
client invalid when attempting to log in.
The cause was that I wasn't passing the host header through Apache because I was missing the
ProxyPreserveHost On directive.
I added this and resolved the issue