For posterity: the data that needed to be different was "4/" vs. "4%2F" for the code parameter. It needed to be the latter now. Presumably there was no slash in the code earlier so it would have worked without decoding.
For posterity: the data that needed to be different was "4/" vs. "4%2F" for the code parameter. It needed to be the latter now. Presumably there was no slash in the code earlier so it would have worked without decoding.