I have until recently been able to send both text messages and images to SMS-contacts from my Mac (10.14.3) over my iPhone (12.1.4). (They have never had iPhones).
Recently this stopped working, now I can only send pure text messages from my Mac, but images are immediately refused with the red exclamation mark and "Not delivered". Clicking then say that "Your message could not be sent. Click 'Try Again' to send this message", and still doesn't work.
I can send both texts and images directly on the phone. I have tried logging out and in again on both devices, reregistering iMessage, but to no avail.
What should I try next?