Since v1 senders will reveal the payment transaction and the use of pj v1 to the directory. Even if the receiver opts out of proposing a payjoin PSBT, and just broadcasts the fallback transaction, this still leaks metadata about use of payjoin and specific versions to the directory.
In order to allow payjoin v2 receivers to require the use of BIP 77 end to end encryption, we should introduce a pjv2 (also available in req-pjv2 variant) parameter, that v1 senders will not recognize. This should have the same exact format as the pj parameter, except fragment parameters are mandatory.
Since v1 senders will reveal the payment transaction and the use of pj v1 to the directory. Even if the receiver opts out of proposing a payjoin PSBT, and just broadcasts the fallback transaction, this still leaks metadata about use of payjoin and specific versions to the directory.
In order to allow payjoin v2 receivers to require the use of BIP 77 end to end encryption, we should introduce a
pjv2(also available inreq-pjv2variant) parameter, that v1 senders will not recognize. This should have the same exact format as thepjparameter, except fragment parameters are mandatory.pjv2parameterreq-pjv2parameter, requires refactoring of bitcoin_uri