Quote from: Charles-Tim on June 17, 2025, 08:24:31 AM

Quote from: nc50lc on June 17, 2025, 04:48:19 AM

You may manually compute it by checking all of its children transaction's "absolute fee" (not fee rate, use a Blockexporer)
Or the lazy method of just going for small additions until you reach the point that it works.

Did you tried it and it worked? It is not working as I tried it up to 600 sat/vbyte. Just one child transaction with 1 input and 2 outputs.

Of course, I've tried that before and did a fresh test after reading this in case there's a bug in the v4.6beta version that I'm using.

Here's a test (testnet4):

I've sent a sample parent @1.43sat/vb (200sat fee) to be bumped in the next step.
Link: mempool.space/testnet4/tx/aa70c7c824294dbee03e5012669406be1bcf273a95511085b328bd7654bddcae (mempool.space may remove the "replaced" note after a while and just show the replacement)
Next, I spent its output with a child transaction @28.4 sat/vB (3100sat)
So to bump the transaction above, it'll have to add: 3100sat on top of its own fee and the new transaction's minimum fee.
Since it was replaced in my test, I've secured a screenshot of that to-be-evicted transaction:
Now for the test, I've bumped the parent transaction's fee to 3525sat which is 3sat more than what is required by the RBF rule. (3100 + 200 + 222 = 3522)
That is where most users get it wrong.
Link: mempool.space/testnet4/tx/5da5e1fb6730edcef66a8a1b0310371b5de00f52367a6ffc5f1836906a1023b8
With it (the parent) being replaced, the child is now evicted from mempools that relayed the replacement parent transaction.
Link: mempool.space/testnet4/tx/a0b1ac2fe240ff230f23fd26f6f5e988cfab6652960d1bf95fd4783cb2d94565 (the txn in the screenshot, now missing)

That's how RBF rules work, if it doesn't work at your end, it may have been to your mention of fee rate since the addition should be based from the child's "absolute fee".
The "Preserve Payment" has nothing to do with the rule, it's just how the user's preference on how to add the required transaction fee.
If it's prevented by that option due to lacking change or other UTXO, he will not get to the point to see that error screenshot that he shared in the OP.

OP's case could also be brought by the server that he's using, because they can enforce higher minimum transaction fee that'll affect the required fee to bump.