FedNow is what has PayPal's former investors so terrified (so much so that investors don't even think PayPal warrants a double digit multiple).
No cost instant financial transfers between US financial users is coming over the next decade. The Fed has 1,400 banks onboard so far, up from 900 the prior year (that's 1,400 in two years). Half of PayPal's business goes away over the coming decade.
We have free instant payments in the Eurozone, UK has had them for about a decade and I'd say PayPal is doing fine (unfortunately). So what's the concern?
Not sure anyone gets an API at no cost for those US transfers ... for person-to-person, they will be/are awesome, but for commerce, pretty sure it will not be a free service.