I suspect that I have encountered the same problem but with a different government site. The US Postal Service (USPS.COM) now requires you to create an account before you can schedule a mail hold. The account creation process requires them to text a verification code to your mobile phone, but that fails with my RW phone. Reading their “fine print” it does say that “landlines” are not supported.
It also gives me the option of going to the local post office and doing this identity verification process in person, so at least I have an option. But this is kind of a pain in the neck and I expect that it will only get worse as more entities start requiring 2FA. I understand that it isn’t something that RW can fix, but it might become a decision factor for RW users at some point down the line.