The most likely cause of this error when converting UP to tez is that the payload you are using is not valid or is malformed. The payload needs to be properly formatted according to the specifications of the contract in order to be accepted. It is also possible that the contract itself is not set up correctly and is causing the error. Make sure you are using the correct contract and that it is properly configured before attempting the conversion. If the payload is correct and the contract is properly configured, then you may need to contact the developer of the contract for assistance.
