16 plus set up icloud verification failed for mail app

I have a new iPhone 16 plus. I have an apple ID with a very old Hotmail email which I only keep as it's my apple ID. That's the one that has my back ups etc. Phone was set up from a back up taken 10 mins prior. I also have an @icloud.com email which I use for all my day to day comms. That is the email account that I have in the "mail" app. I am trying to set the mail app up and it is asking for my apple ID password for the icloud account which I am entering (have successfully changed this password for today to ensure I wasn't entering it incorrectly. when i enter the password i am continually getting an error message " Verification Failed. Unknown error occurred" any suggestions on how to fix this? Very frustrating! thanks :)