I was able to identify the source of my problem. The following is what is being called in my Postman script
var key = CryptoJS.enc.Base64.parse(mastKey);
But I can find no equivalent in Informatica's functions. The util:base64Decode seems to be the only option that is close, but does not return the same values. I may be at a dead end using this approach.
Do you know the difference you see between the value you get using CryptoJS.enc.Base64.parse(mastKey); and infa function util:base64Decode ?
I will include the screen prints for easier understanding especially with the non-printable characters showing. The source code making the original calls are also shown. 1st Image is the Postman call and Postman Console. 2nd Image is the Informatica call and 3rd Image is the Rest Request showing the value. Thanks for taking a look.