MMS Issue

I have TMobile Home Internet. 95% of the time I use wifi for my cell phone, which is a Google Pixel7, not 7Pro, just a 7. I have a small data plan with MVNO carrier Mint Mobile, which uses TMobile towers I understand. My plan is tailored to the expectation that other than 5% of the time when I am out of wifi range and/or outages (which used to happen frequently when I was with Windstream), I would not have my mobile data even turned on. 
Out of the clear blue MMS would not send or receive thru TMobile. I had to have my Mint Mobile data plan turned on. It has been like this for a month now. I have thoroughly checked all APN settings with Mint, who claim they are correct for my phone. 
I need this resolved. Is this a TMobile issue and if so, how do I fix it?
TIA.