The return value of a call to an App Script returns an array of objects in the following format:
[{"a":1,"b":2,"c":3},{"a":1",b":2,"c":3},{"a":1",b":2,"c":3}]
How does one use the return value to populate the rows of "Table1" with columns "a","b","c"?
I'd recommend processing that in the script itself, either adding the data directly to the source, or sending it through the Appsheet API.
My go to (very high level):
It looks like you've got the basics there, just a matter of changing the JSON objects you're creating to those for the API add action.
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FYI: You CAN specify that the return is an object (in AppSheet, when executing a script from a bot)
Then you can use the de-reference formula you see in the gif at the bottom (in blue)
In a follow-up step you can use that formula: