Made the payment address (aka payment secret) flag required in our invoices (and also
the TLV onion as payment secret depends on it). Having the flag as optional was causing some strict
services to block zero amount invoices from Muun. If the secret is optional, the last hop (us) can
forward a fake sphinx without a payment secret and for 1 sat, the app will accept it since the
secret is optional and the last hop keeps the rest of the payment. Payment secret has been widely
adopted for quite a bit now. Major impls all require it.
[51.8] - 2024-02-23
CHANGED