First, make sure that your url is accessible.
If it requires username and password then set them accordingly in
httpPassword parameters and try again.
If you use Google Docs, Google Drive then make sure that the link to a file or a document is not requiring to login. Try to copy the link and open in Incognito Mode in the browser to see if it opens OK.
If you are getting
Too Many Requests (or sometime
Access Denied from Google Drive/Docs/Sheets) then try to add caching for the input file. To enable caching please insert
cache: before the link.
https://example.com/file1.pdf with caching:
NOTE: caching will not be fetching the original file but will cache it in PDF.co and will be reusing the file in next 15 minutes without making a request to the original url.