IONOS webmail

My ionos webmail has stopped syncing on my iPhone. I'm getting no where with apple support or ionos support. It randomly stopped syncing 2 weeks ago, i have reset, deleted and reinstalled countless times. I've made sure all server settings are the same across the devices, but still they are not working.

I should add that I have multiple IONOS emails on my device and it is just on one account (my main one, sods law)

• iPhone is running iOS 14.2 (recently updated to try and solve the issue, problem happened before update)
• MacBook Pro (Retina, 15-inch, Mid 2015) is running version 10.14.5

Happy to send as much info as possible to sort the issue, any help is hugely appreciated!