Messages app (v 14.0 on MacOS Sonoma) does not send images

I've recently updated to MacOS Sonoma, and when I'm attaching a photo to an iMessage, it appears to be sent on my side, but on the recipient's iPhone it does not appear, and no notification is sent to the remote device. I cannot even see the message on my phone. However these images can be seen in Messages on my Mac even after restarting the app. If I forward my own message (with the image) to the same recipient, the forwarded attachment magically appears. But if I drag-and-drop an image onto Messages or of I copy and paste an image or if I try to send a pasted screenshot to anyone, the behaviour is the same. It is very annoying. Does anyone else has the same issue?