Check the file size first
Uploads over your plan's maximum file size are rejected. On Easy Start that's 100 MB per file; on Professional and Enterprise it's 1 GB. See Storage and file size limits.
This is the most common cause by a wide margin, and it usually means the client photographed a long document at full resolution or is sending a video.
Ask them to scan in black and white, lower the quality setting, or split the document and send it in parts. Upgrading the plan raises the ceiling if it keeps happening.
Check the item's file type
An item set to one kind of file (PDF Only, Images, and so on) refuses anything else in the portal: the client sees a red line naming the file and it isn't uploaded. If they only have the wrong kind, either change the item's accepted file type with Edit Checklist, or point them to Scan with Camera, which makes a PDF from phone photos when the item takes PDFs.
Check the link
Confirm they're using the most recent link. If you've since sent a newer request, an older link may no longer work. Resending the request gives them a current one.
Also confirm the link went to the right address — an old email on the contact record sends the request somewhere they never see.
If you or a colleague archived the contact or the request, its portal links stop working on purpose and the client sees an expired-link message. Restoring the contact or request brings the same links back to life.
Check their device
If a phone upload fails repeatedly, ask them to try a computer, or vice versa. Unstable mobile data is a frequent cause of large uploads failing partway.
Send them the client guide
My upload isn't working is written for your contact rather than for you, and you can send it to them directly. Photographing a document with your phone is worth sending too if they're struggling with camera captures.
If none of that resolves it
Email support@docevault.com with your organization name, which request and contact are affected, roughly how large the file is, and what device and browser they're using. That's enough to reproduce it.