That's not good.

I realized that I was not double hashing the outpoints list before putting them in the sighash, but I still get an error.

Sighash for a new transaction (before signing):

0100000046111bba17bad101669337a4c13f11953520347f16e5757949e9bebf52d01a068f64b0c 3a7d964081e85a1401845112be7ea0c37947b7e57a9dc74a20ff19dc294dabca706fe011969ea96 490924a40e961d7573af034d28513718d6b9dccc2f0000000076a91480f785495c8f30a13402ca3 37b21f6d5c65fb0f688acfacfff05000000000000008055c6c38707420170e30c334bcc539feec4 e469bdab6711dddff92ef11e97ba3c0000000001000000

Version is 1, hashPrevouts (before double hashing) is 94dabca706fe011969ea96490924a40e961d7573af034d28513718d6b9dccc2f00000000 [i.e. the input is txid 94dabca..., #0]

hashSequence is 00000080 (note: It is not 0xffffffff because I want to use RBF, but it should mean that timelocks are not enabled)

hashOutputs is 021027000000000000160014c2229d66eeff61900b4678b23853e0a8502df56a000000000000000 0160014c2229d66eeff61900b4678b23853e0a8502df56a (the single output of this transaction along with script pubkey)

The script added (directly without hashing is 76a91480f785495c8f30a13402ca337b21f6d5c65fb0f688ac - P2PKH script, since I was told that P2WPKH UTXOs requie this

Locktime is 00000000 and sighash type is SIGHASH_ALL ie 01000000.

Sorry for the really long output, I'm really confused here to be honest