Hi @dna.pc.pro, thank you for the all detailed information provided.
The Airtable API expects a list of up to 10 URLs for attachments. You can use the following code below if you want to upload just one attachment URL:
{{ [ { "url": "https://www.africau.edu/images/default/sample.pdf" } ] }}
Explanation:
The prop will load the input value as a string, so we need {{ }} to actually send it as a JS object.
Then we send a list of objects { "url": "http_url" }.
I believe you correctly tried the example above, just not encapsulated the object inside an array. Please try this out and see if it works for you!