* Since you are the administrator: there's noone else for you to contact. Good thing you've had a little bit of practice with PHP. Fix the error so that you can log in to your Nextcloud installation. [https://help.nextcloud.com/t/howto-add-a-new-trusted-domain/26 This Nextcloud help page] might help too.

You've been using public key cryptography for your entire life (unless you were born before the 1990s). You've been setting up public key cryptography since at least OPS245. Let me encourage you to actually understand how that stuff works.