How do I output the results of an array as a String?

Here is my Input Field in a form. Blank, with a placeholder.

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Here is my Server Action with $_POST as my expression for a repeat. Then, in the repeat, Set Value for a variable called parts_results.

The results in DevTools is exactly what I want to see in the resultant Input Field.

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But my resultant Input Field only displays a full-stop! As shown in the Server Action above.

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Because the full-stop is showing, just proves that something is working.

Why am I not getting the full results?