Indonesia is still part of KF-21 program, if it buys Su-57 we should soon hear something.
Payment should be less of a concern as bilateral trade in local currency is becomging more of a thing. For example China and Indonesia began trade in RMB and IDR since 2021, it is not only China want to do so but also Indonesia. No reason that Indonesia and Russia not doing the same. These trade does not go through SWIFT, so US would have no way to know nor any way to block it even if it knows. The same applies to all potential buyers.
The only question is that how does Indonesia judge Su-57 over KF-21's price/performance. KF-21 isn't in production yet and it is only a quasi stealthy figher even if it has better workmanship and the critical shortcoming the US engine. The only thingthat Indonesia can get from the KF-21 is to improve its competence in the industry. It would be stupid to actually equip KF-21 in large numbers or at all. This means that US lifting block isn't going to make a difference.
The true uncertainty for Su-57 sale to Indonesia is J-35A.