From what I understand, you’re trying to send a list of Things (in your case, a Permission) to an API service. Is that correct?
There’s a few ways to do this, but you need to make sure that the privacy rules for your data type (Thing) Permission allow for this.
One way that I like to do this is to make an expression that uses the :format as text operator. For example,
Do a search for Permissions:format as text
This will allow you to define some text for each item. What you can do is:
{ "field1": "value1", // Add any values you want here }
And make sure to choose “,” as the delimiter.
This returns a list of JSON objects (if you did it right). You can now include this in your request body.
Important : Do not open the rich text editor when doing this. It completely breaks the JSON formatting for some reason, even if you make no changes.
Good luck 
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