How to save an Image to a file via WriteLine ?

Hello all - I'm on Peoplesoft FSCM 9.42.47 with Peopletools 8.59.23.

My issue is that I'm having trouble getting and saving to a file, a Binary response of a REST API. It is an Image, JPG.
I expect to retrieve the Binary value from the API - and I think that part is working in an App Pkg class-
I pass the field to the App Engine pcode via an AET file,
but then I can't seem to get around errors when I try to WRITELINE the Binary field in my App Engine pcode.
-->> This line isn't allowed to save: &out_document_file.WriteLine(MAM05704_AET.BINARYSTREAM);