When saving "Parse Single Response Output" to a variable, if "Use Array" is checked and the output variable contains underscores, using the output variable in post-process causes the RA REST job to fail with a FAULT_POST_PROCESSING status. The details of the job show the following error:
U00021719 Syntax error in object '<Webservice_REST_Job_Name>', line '00000'. 'U01001344 The total array '<Output_Variable_Name>' must not be indicated here.'.
The maximum number of characters for the array variable (24) has been exceeded.
Shorten the variable name so that the array name (including leading '&' character) is less than 24 characters.