Hi,
Just curious what you meant by the text box is too short? Are you trying to enter a lot of data into the actual box on the operator?
One of the ways I populate large amounts of data is to store it in an operator variable (usually in the pre-exec code) and then pass that into the operator with (example) Process[OpName].RestBody
Also, I often use PowerShell to run my Http/Rest requests, as you can easily make those calls there.
Not sure if this helps you with your issue, but thought I'd mention it.
Ian