Can't connect with AT&T PPP?

Does AT&T supports the Cellular IoT HAT?
We are testing the Verizon version on Verizon network and it’s working great. Super stable connections.

However, the M2M Verizon pricing is nuts. We discovered that AT&T offers unlimited data plan for around $35 - https://marketplace.att.com/products/att-lte-m-one-rate-plan

I’m not able to find SixFab or Quectel BG96 as a certified device or chipset on their approved devices list.

Thanks
Radek