Variant of this I've hit is the phone number validation rules at signup differs from the actual API call to send 2FA texts (or was changed between the time of original signup and login attempt) so I create an account successfully with a Google Voice number and then when I actually need to receive 2FA the message goes into the aether with no error surfaced at any point.
> Variant of this I've hit is the phone number validation rules at signup differs from the actual API call to send 2FA texts
Yeah, this is incredibly annoying, though to be fair, this can be a hard problem to solve. 3rd-party systems often don't tell you what their exact phone number validation rules are or silently update them, and then, to top it off, don't throw errors when validation fails. And more often than not, the 3rd-party system's developers also must have never heard of the Falsehoods programmers believe about phone numbers[0].
Source: I was responsible for adjusting phone number validation for a major ecommerce site in the past.
