iOS Mail-app: Please enter gmail password when using alias. Works with other account, but not with this

So I have just made a new email-adress to use with my buisness the exact same way I have set it up with my private email-adress. Both emails are through domains that I myself own and both mails are set up to "filter" through a gmail-adress. So, the mail account in both MacOS and iOS is first setup with the standard gmail-setup. So far so good. For my private adress on both my mac and my iPhone I have simply just changed the outgoing mail-adress to be from my domain (not gmail) and it works flawlessly. I get all my incoming mail filtered through gmail and when I send emails, they are sent from the other adress.

The same goes for sending and receiving emails with my buisness adress on my mac, but for some insane reason NOT when receiving emails on my iPhone with this setup. I get an error at it wants me to enter my gmail-password. There is no way to enter the gmail password since it's an automated setup. I can send emails from my domain-adress, but since this adress is the one registered in the mail-settings, it suddenly wants me to enter a password even though there is no way to do it. When changing the gmail-account mail back to the gmail-adress I can receive mail, but now I don't have the option to send from my domain-mail anymore.

Can anyone help me out here? Both the private and buisness accounts are set up the exact same way as far as I can tell. Have checked all setting on the iPhone, on gmail and on my other domain.