How can I get AMP approval for my emails?

Hi all! I'm working on getting AMP approval for my company. After fulfilling all the preliminary requirements, I sent an AMP email to their whitelisting addresses.

However, they informed me that my email wasn't approved because it did not have a "text/html" or "text/plain" MIME part that looks similar to the "text/x-amp-html" MIME part.

I can see the text/plain version of the email when I toggle my campaign to a plaintext editor in Braze so I'm unsure about what is missing in the email itself that wouldn't comply with their requirement of having a "text/html" MIME part. 

I've reached out to them and they haven't responded yet so I'm hoping someone on Bonfire can provide guidance for how to get AMP emails approved.

Thanks in advance!