If attachment thumbnails appear then disappear (or seem to delete themselves), that means your URLs are invalid. To convert URLs to attachments, the file link needs to be:
1. Public
Make sure those URLs are publicly accessible, not protected files behind a login page. If you use a private URL, the login page will be fetched instead of the actual file.
2. Direct
It cannot be a link to a file previewer webpage. E.g. it should end with a file format like .jpg, .png, .pdf, etc. Try to open the link in a private window on your browser. A file should start downloading (or displayed if an image).
⚠️ Note
It might look that the files are being uploaded successfully and then deleted. But in reality, there's nothing to be uploaded. When the attachments 'appear' in Airtable and then disappear immediately, that doesn't mean the attachments are being removed. It means the uploading URLs are not supported.
💡How to test my link?
We wouldn't be able to tell why the process is failing. To find where the issue is:
Make sure the link is still working by opening it in your browser.
Try testing your URL using the attachment uploader in Airtable. This will help you narrow down the problem.
If you're seeing the same issue in the Airtable uploader (e.g. blank pdf), this means the problem is not the extension itself. It could be in Airtable or the source that's hosting the URL (e.g. Dropbox).