Steps to reproduce on regtest:

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

Further reading: #13738
RPCResult{
                            "  \"psbt\"        (string)  The resulting raw transaction (base64-encoded string)\n"
                },
                RPCExamples{
                    HelpExampleCli("createpsbt", "\"[{\\\"txid\\\":\\\"myid\\\",\\\"vout\\\":0}]\" \"[{\\\"data\\\":\\\"00010203\\\"}]\"")
                },
            }.ToString());
    RPCTypeCheck(request.params, {
        UniValue::VARR,
        UniValueType(), 
        UniValue::VNUM,
        UniValue::VBOOL,
        }, true
    );
    CMutableTransaction rawTx = ConstructTransaction(request.params[0], request.params[1], request.params[2], request.params[3]);
    
    PartiallySignedTransaction psbtx;
    psbtx.tx = rawTx;
    for (unsigned int i = 0; i < rawTx.vin.size(); ++i) {
        psbtx.inputs.push_back(PSBTInput());
    }
    for (unsigned int i = 0; i < rawTx.vout.size(); ++i) {
        psbtx.outputs.push_back(PSBTOutput());
    }
    
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
}
UniValue converttopsbt(const JSONRPCRequest& request)