@LoudLemur looks like the DNS record was pointing to a Cloudron which didn't have any app installed on that (sub)domain. If a Cloudron server as such just gets deleted, then the DNS records are not automatically cleaned up, since there is nothing running anymore to do that.

Looks like they loaded suddenly for me.

What your images show seem to be all the right places to put the new/changed secret. Also note that after changing the two places in the onlyoffice config file, you have to restart the app to pickup those values.

Further your pasted curl error, from which part is that error coming? Nextcloud or is this a manual curl command you are running? For the latter, can you maybe pass -v to get more verbose information?