Can't send or receive MMS messages.

Hi.

I've recently (about three weeks ago) moved from an iPhone SE to a CAT S41 running Android 8.0.0 . I've quite enjoyed moving from the dark side, but can't manage to get the phone to either send or receive picture messages from the default messaging app (it just says 'sending' for a long time until it eventually fails).

I've turned off imessage on the old phone, and tried rebooting several times. Standard texts work fine, as to pictures and videos on other platforms like WhatsApp and Messenger. The problem's the same whether I'm on wifi or not.

Any ideas at all?
Thanks.

Check that the APN (in Settings > Network > Mobile network > Advanced > Access Point Names) is set properly for your carrier. (One or both of the MMS lines are probably wrong.)