Your proposed approach is not practical:
Users might change the amount, or omit the fractional part
The fractional part might represent significant value - a user with an ID of 1234567 will have to pay a minimum of 0.01234567, well over a hundred USD at the moment
If users are withdrawing from an exchange or some other wallet without much control over the ...
Conversion from a HD seed to a master private key is specified by BIP 32.
It is done by computing a HMAC-SHA512 where the key is the text Bitcoin seed and the data is the HD seed itself. The first 32 bytes (256 bits) is the master private key. The last 32 byte is the chaincode for the master key.
You could also load it into other clients such as Bitcoin Core if you convert the seed phrase to a WIF-encoded extended private master key (112 byte base58 string starting with 'xprv')
Not sure if it offers a way to easily do that, such as dumpwallet in core, I wouldn't just go entering it into any webpage offering to convert it for you, but it's pretty ...
Why was the fingerprint chosen for psbt instead of the full hash? Collisions aren't that rare for just 4 bytes of data and adding mitigations in the psbt transaction parsing for such a case seems unnecessarily complicated.
Fingerprint collisions would still require thousands of signers in a single PSBT to actually be a problem. Collisions aren't all that ...
bitcoin-cli is generating a P2WPKH address (bc1...), but then on the user side you are generating a P2PKH address (1....).
You may also need to check to ensure the same address derivation path is being used (Bitcoin-core uses hardened derivation).
For more info on address encodings see:
What is P2PK, P2PKH, P2SH, P2WPKH - ELI5
What is the size of ...
I want to know why the two tools are giving different results
Bitcoin Core uses hardened derivation to derive child private keys from the master private key. You can check the embedded link for more details, but in summary it means that the software uses parent private keys within the hash function to generate child private keys. This compares to non-...