When mapping fields within an action (SQL Server, HTTP, etc) you may run into an error message where part of the error includes the below text.
call is not a function
The first thing to review is whether your variable reference has a space in the name similar to the example below.
To resolve the issue, please remove the space from the key if possible. If you are unable to remove the space from the key due to other system dependencies you will need to change the above reference to match the structure below using the "Other" transformation option from the drop down menu.
Note: The main change is the square brackets and double quotes around the key
Example screen shot for the above scenario.