In OCPP 1.6 the transaction IDs are 16-bit integers, generated by the Central Service. In OCPP 2 the transaction IDs are strings (up to 36 characters), generated by the Charge Point. To support both models, update SN to treat the transaction IDs as strings. In OCPP 1.6 16-bit integer IDs should still be generated, but stored as strings and converted to integers in the OCPP 1.6 API as needed.