iMessage: iPhone 'not delivered', Mac/iPad 'delivered

I've been having issues with imessage for a while now. It says "not delivered" with a red exclamation mark on my iphone (iphone 11, updated with the latest software), but it's marked as delivered on my macbook and ipad (ipad air 4th). additionally, I only have an issue with this particular contact, all the other ones are fine.

Does anyone know how to fix this?