Alchemy - replacement transaction underpriced

Question

SC: 0x3c445903aCa6c4d1B55357Fb9F8e22252899478A

I simply try to mint() on Polygon Mumbai but I had to workaround "replacement transaction underpriced", I still can't see any pending/unmined Tx..nor do I see a Nonce issue

I fixed it by increasing gasPrice to 50 gwei but:

1. Could help me understand where was the unmined/pending Tx that was blocking? I could see nothing on the Dashboard nor on PolygonScan
2. I used to be able to send my Tx without setting up the gas attribute, why is it necessary now?

this is my code:

PS: 27256 didn't help as it just shows how to fix by trial and error imo

Thanks a lot for your help!

Answer 1

Polygon's Bor client (currently a modification of Geth) uses the same default value setting for replacement transactions that you can view here.

What this means any Polygon node running in the default setting has the priceBump value set to 10. This in turn means that to replace a pending transaction you must submit a new one with the same transaction nonce but the fee that is higher than 10% than the pending one. If you submit with the same fee or the fee increase is lower than 10%, the node that you are using to send your transaction will reject the transaction with the "replacement transaction underpriced" error.

There are node providers that allow for custom settings, including the priceBump node setting. e.g. Chainstack.

As to why you didn't see your pending transaction on polygonscan it might be because your transaction didn't enter the mempool of polygonscan nodes.

If curious, you may want to read and explore all the EVM mempool stuff here.