The lede here is somewhat burried:
"From what I’ve since learned, if a card in your Google Pay is stolen, or someone uses your Payments account fraudulently, or anything happens that leads to a security flag being raised, it can lead to your Google Payments account being frozen.
...
If you can’t use Google Payments, you can’t pay for Google Fi
This, fundamentally, is why I can’t suggest anyone use Project Fi anymore.
...
Getting this fixed is actually impossible, and I say that as someone who really, truly, loves solving problems and has made a living off getting phone agents to want to help me.
We have submitted copies of his ID four times, my ID twice, multiple photos of credit cards, and various credit card statements. We’ve talked to agents and supervisors at Google Payments and Google Fi. No one is empowered to do anything, and even a well-intentioned agent doesn’t get the same answer from the “security department” twice.
I’ve since found hundreds of comments and Reddit threads from people having similar experiences, with almost zero positive conclusions.
The only suggestion of a solution we’ve been given is that he abandon both his email address and phone number of the past twenty years and start fresh."