Thanks Kolban. You were certainly on the right track to mention the different parameters that were being passed to the API from the make.com module.
What I noticed was that the error only occurred when I used one of the Neural2 voices such as the en-US-Neural2-A [MALE] voice.
When I switched to one of the other voices such as the en-US-Studio-O [FEMALE] voice everything worked fine with no error:
I found mention of an ongoing internal bug for this issue. My issue is resolved since I don’t need the Neural2 voice to work, but it still seems odd that this bug exists.