Unclear initial scan: Sometimes, fax-sending issues can arise if the initial scan of the document is unclear or of low quality. However, there might be other causes if the preview appeared fine.

Poor internet connection: Faxing over the internet relies on a stable and adequate internet connection. A good or reliable internet connection on either your end or the receiving fax machine's end can lead to transmission problems.

Old or poorly maintained fax machine: If you're sending a fax to a very old or poorly maintained fax machine (the most often reason), it may need help to receive and process incoming faxes, resulting in issues.

Check the quality of your document: Ensure that the document you are sending is clear and legible. If necessary, rescan the document to improve its quality.

Verify your internet connection: Make sure your internet connection is stable and functioning correctly. If you suspect an issue, consider testing your internet speed and troubleshooting any connectivity problems.

Contact the recipient: If you suspect that the receiving fax machine might be old or in poor condition, it's a good practice to contact the recipient or the organization to verify their fax machine's functionality. They may be aware of any issues on their end.

Try resending: Sometimes, a transient issue could have caused the problem. Try resending the fax to see if the issue persists. Ensure that all the details, including the recipient's fax number, are correct.