Steps to reproduce on regtest:

```
converttopsbt 02000000000101ab73dba46508bacdb49a988ddd74bc9d39c9cb7e057af060ca8c6b6861e28e3c0300000000feffffff02b828d0b20000000017a914d1954862afd728fbb055149002958e1d1b9e1f0b8700ca9a3b0000000017a91442170ccb3441cff1723af9afab6f2553103e1d578702473044022077380c6e16496d9905aef120694c329be51522847cb5d53fa74b94698c95678d02202d32c46e0e17420a83dee830fefda7d40529182f5d82be47c2b49a7b83214ab50121026d483d6628dcc3ef6e3ab9ed4937c452c263c7e0ac80eb4be97426d5da8f640500000000
```
or 
```
converttopsbt 02000000000101ab73dba46508bacdb49a988ddd74bc9d39c9cb7e057af060ca8c6b6861e28e3c0300000000feffffff02b828d0b20000000017a914d1954862afd728fbb055149002958e1d1b9e1f0b8700ca9a3b0000000017a91442170ccb3441cff1723af9afab6f2553103e1d578702473044022077380c6e16496d9905aef120694c329be51522847cb5d53fa74b94698c95678d02202d32c46e0e17420a83dee830fefda7d40529182f5d82be47c2b49a7b83214ab50121026d483d6628dcc3ef6e3ab9ed4937c452c263c7e0ac80eb4be97426d5da8f640500000000 false
```

Further reading: #13738
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
        throw std::runtime_error(
            RPCHelpMan{"finalizepsbt",
                "Finalize the inputs of a PSBT. If the transaction is fully signed, it will produce a\n"
                "network serialized transaction which can be broadcast with sendrawtransaction. Otherwise a PSBT will be\n"
                "created which has the final_scriptSig and final_scriptWitness fields filled for inputs that are complete.\n"
                "Implements the Finalizer and Extractor roles.\n",
                {
                    {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"},
                    {"extract", RPCArg::Type::BOOL,  "true", "If true and the transaction is complete,\n"
            "                             extract and return the complete transaction in normal network serialization instead of the PSBT."},
                },
                RPCResult{
            "{\n"
            "  \"psbt\" : \"value\",          (string) The base64-encoded partially signed transaction if not extracted\n"
            "  \"hex\" : \"value\",           (string) The hex-encoded network transaction if extracted\n"
            "  \"complete\" : true|false,   (boolean) If the transaction has a complete set of signatures\n"
            "  ]\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("finalizepsbt", "\"psbt\"")
                },
            }.ToString());
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL}, true);
    
    PartiallySignedTransaction psbtx;
    std::string error;
    if (!DecodeBase64PSBT(psbtx, request.params[0].get_str(), error)) {