Can't send or receive MMS on iPhone 8 Plus on Verizon if on WiFi calling
An iPhone 8 Plus can't send / receive MMS messages (i.e. non-iMessage group messages) when on WiFi calling


This is expected.

WiFi calling has no provision for sending either SMS or MMS messages that’s a function of the GSM Network.  Also, MMS is multimedia messaging, not “non-iMessage group messages.”  Now, as long as you’re connected to WiFi, you can receive iMessage messages.


  In case it's relevant, there is extremely marginal cell tower coverage at this location (i.e. ~1 bar).


It is relevant if you have your cellular on, but signal is so low that you’re using WiFi calling instead.  SMS using a very small amount of bandwidth compared to MMS, so it’s entirely possible regular SMS messages go through and MMS messages do not.  Also, unlike SMS, MMS will typically not queue up and continue resending; they usually delete after a period of time, sent or not.