I have two domains, the first one updates OK, but the second fails with bad authorization. Since both domains are on the same account I've used the same username/password for both accounts but the first one works and the second does not. I've tried using the password for the WordPress wp-admin of the second site but that does not work. Also I've set ssl=yes, one for each account - or does only the one matter?
Also do I have to restart the service when I make changes to the conf file?

What IP update software are you using?

Sounds like you are using DDClient. If so, you can refer to the config file at https://www.dynu.com/DynamicDNS/IPUpdateClient/DDClient. The password should always be the Dynu account password or IP update password.

You do need to restart the service after making changes to the config file.