Yeah I managed to get it working using the Govern workflow I posted in the previous post.
1) Step 1 is the original Action form with then hidden comments field

2) Step 2 is the email sent to the approver.

3) Step 3 is the form sent in the email

4) Step 4 is the creation of the new asset using the comments from Step3 / Approval Form

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The field change node in the Govern workflow is the key to swapping the value. The output will show FALSE as mine does below, but the value will still update on the form.

What response code did you get from the HTTP node?

As you can see from the screenshot above, I did manage to use that comments field from the approval form to add in as the action form field in the POST payload.
Did you see your asset created without the comments? or did it fail to create at all?