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ORA-08458:

invalid format parameter
Cause: The format parameter passed to a UTL_PG conversion routine was invalid. The format parameter should have been built by a prior call to either MAKE_RAW_TO_NUMBER_FORMAT or MAKE_NUMBER_TO_RAW_FORMAT.
Action: Check to be sure that the format parameter was built by MAKE_RAW_TO_NUMBER_FORMAT or MAKE_NUMBER_TO_RAW_FORMAT, and that it was not accidentally overwritten or modified by the PL/SQL procedure.