Yeah, been through that document already, if it were something that simple, I wouldn't be posting here.
Your subscription has run out - double check this on the vpn providers website.
-nope, logged into the site today, I have over a year left
You have not typed in your username and/or password - do not copy and paste, type it in manually to prevent whitespace issues.
-nope, copy/pasted, manually entered, regenerated credentials, and retried several times, this is not the issue
You are using the wrong credentials - ensure the credentials are for openvpn/wireguard, NOT proxy servers etc.
-this is the only 'maybe' here, I can't tell if PIA uses different credentials for wireguard, and if so, I can't find them, but I was getting the error for openvpn as well as wireguard, so either way this isn't the issue for at least one of my attempts and both are having the same issue.
Your password contains a character which may cause issues - please ensure it only contains letters a-z (upper case or lower case) and numbers 0-9.
-nope, using credentials generated by PIA, no unusual characters
Out of date openvpn config file (ovpn extension) - ensure you download the latest ovpn file from your vpn provider.
-nope, fresh download, files are dated 8-11-20, from the next-gen zip file
The vpn provider you have signed up with is having authentication issues - try another endpoint, failing that contact the vpn provider and explain you are having authenticaiton issues when using native openvpn/wireguard clients with AUTH_FAILED shown.
-maybe, but I'd expect a company as big as PIA to have that somewhere public if their connections have been down for days... Tried about 5 different endpoints, all give the same issue.