IMessages not synchronising to new iPhone

I have an unusual problem where my iMessages don’t show up in messages on my iPhone. This is a new iPhone and the previous phone worked fine.

I have several other devices (2x MacBook and 1x iPad) where the iMessages show up fine.

On the iPhone my iMessages will send and i can see iMessage replies in notifications but when i click into the conversation they are not there. Only text messages.

I have checked all devices are set to sync, signed out of iMessage on all devices, turned off iMessage on all devices and multiple restarts on the iPhone with settings enabled and disabled. No joy. Every other device syncs again and messages show up fine, except the iPhone.

I have no more ideas - help appreciated! This problem makes messaging very difficult and I am missing important conversations.

Thanks

Ben