On the web
Refresh the page.
Sign out and back in.
Try a private/incognito window. If that works, an extension, often an ad blocker, may be interfering.
Use an up-to-date Chrome, Safari, Edge or Firefox.
On iPhone or Android
Fully close and reopen the app.
Update to the latest version from the App Store or Google Play.
Check your connection. Uploads resume once you're back online.
Still broken? Report a bug. It sends us the technical details we need.