iMessage Failed to Send notification on the lock screen every time I turn on the iPhone

I tried to send an iMessage with an image a few days ago, it failed to send therefore I deleted the message entirely. Now every time I turn on the iPhone I keep getting this annoying message on the lock screen. How do I make it stop, its infuriating?

When I go to apple iCloud on settings, select iMessages, synced is ON, however when I try to unselect 'sync this iPhone', I receive a 'Messages have not been fully downloaded to this iPhone', which I can't rectify, how to resolve this? I've tried 'disable and download messages' option, it didn't work.

I have tried everything to no avail:

Logging out of icloud and signing back in - Done

Turning iMessage notification off and on - Done

Deleting the iMessage conversation - Done

Restarting iPhone - Done

Reset network - Done

Tried disabling notifications for the Messages app, restarting my iPhone, and then enabled setting again - Done

I don't want to permanently remove notifications (which stops the message), I have plenty of storage.

I'm using a iPhone 15 pro, IOS 17.0.03.

If its because my carrier (EE in the UK) doesn't allow messages with images, I've just purchased extra credit and still not sure what to do.