I have an iPhone SE (old model) and a 12 Mini. I had no problem purchasing a one-year card on the website for the SE. When I tried to do the same with the 12 Mini, I got this message:
Our partners are upgrading their network to provide you with the highest quality service. Unfortunately, this phone is not compatible and can't be activated.
But don't worry, because we're offering you $40 off any phone purchase of $40.99 or more today! Just call us at 1-800-867-7183 to get your offer.
This is obviously wrong. I've been using the 12 Mini for over a year on TFW. And when I called TFW from a landline and put in my phone number, the automated system allowed me to purchase a one-year card.