Unclear initial scan: Sometimes, fax-sending issues can arise if the initial scan of the document is unclear or of low quality, including low resolution, out-of-focus scans, shadows, or skewed pages. However, there might be other causes if the preview appeared fine.

Lighting and contrast issues: Glare, uneven lighting, or faint text in the original document can cause the app to misinterpret the image during binarization (conversion to black-and-white).

Poor faxing line connection: Connection interruptions on either the sender's or the recipient's side 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. Use the app’s document scanner instead of taking photos with the camera, and enable features like edge detection and contrast enhancement. 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. Additionally, ask the recipient to check their connection if issues persist.

Improve lighting conditions: Use soft, even lighting and avoid glare, especially on glossy documents. Avoid pointing direct light at the document to prevent bright reflections.

Enhance image quality before faxing: Use an image editor to adjust contrast and sharpness. Place a dark, non-reflective sheet behind thin pages to boost contrast. Rescan or re-import the improved image into the app.

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.

Change the File Format: Resending the file in a PDF format can improve the image quality.

Use Online Conversion Tools: Online tools can help adjust the file format or image settings, improving the fax's quality.