nts:
1. psbt       (string, required) A base64 string of a PSBT
2. extract    (boolean, optional, default=true) If true and the transaction is complete,
              extract and return the complete transaction in normal network serialization instead of the PSBT.

Result:
{                             (json object)
  "psbt" : "str",             (string) The base64-encoded partially signed transaction if not extracted
  "hex" : "hex",              (string) The hex-encoded network transaction if extracted
  "