JotForm might not support sending attachments to Airtable, since Airtable requires a public URL to download its attachments from.
You might want to ask JotForm about this, and be sure to let us know what they say!
If JotForm doesn’t support sending attachments directly to Airtable (because Airtable requires a public URL to download its attachments from), then you would need to use an automation tool like Make to sit as the middleman between JotForm and Airtable.
So instead of sending your JotForm submissions directly to Airtable, setup Make to watch for your submissions, then upload the attachment to a publicly-accessible cloud drive, grab the URL from that file sitting in the cloud, and then you will have everything you need to create the new record in Airtable.
Note that I haven’t tested any of the below — I just whipped together this screenshot really quickly to show you what I would envision your Make scenario might need to look like. But I’m not sure if you would need to add extra steps or not, because i haven’t tested this at all: