I see. That https://github.com/lightning/blips/pull/18 is not merged since 2022. Looks like there is a simpler and less disruptive way to implement that and it is to ask the peer on the other end of the channel to lower their fee and you will pay the diff to them. For example, assuming a channel between A and B:
A (outbound fee 1000) ---> (inbound fee -100) B
would be the same as:
A (outbound fee 900) ---> (no inbound fee, B pays 100 to A after a payment goes through) B
In the second case a greedy and mean A can increase the fee from 900 to 1000 shortly after and get 1000 from the sender and 100 from B. But that is equivalent to the first case where A can increase its fee to 1100 after noticing B set -100 inbound.
Inbound fees have to be supported by all softwares that support sending payments over LN. I wonder how many support that currently.
AandB:A (outbound fee 1000) ---> (inbound fee -100) BA (outbound fee 900) ---> (no inbound fee, B pays 100 to A after a payment goes through) BAcan increase the fee from900to1000shortly after and get1000from the sender and100fromB. But that is equivalent to the first case whereAcan increase its fee to1100after noticingBset-100inbound.