If your activity doesn't appear on Strava after recording it in the iOS or Android app, try the platform-specific steps below to get it to sync. If you record with a GPS device instead of the Strava app, see How to Get Your Activities to Strava for device-specific syncing help.
Android
Try recording a new activity, saving it, and uploading it to see if that pushes any missing or pending uploads to your account.
Make sure you're in an area with good data coverage or, even better, connect to WiFi, then tap on the activity to try again.
Log out of the Strava app, then log back in.
Turn your phone off and back on again.
If you're still having trouble, your phone may show Unsync'd Activities in your feed. Select Unsync'd Activities, then tap Sync to prompt your phone to try again. You can delete the failing upload, or export the activity as a .GPX file to your phone's internal storage and email it to yourself so you can upload it via the Strava website.
It's also possible that your phone's available storage capacity is causing the sync issue. Syncing needs additional storage to process the recorded data before sending it to Strava's servers. If you're running low on space, try removing some photos or music to free up enough space for the sync to complete.
iOS
Try recording a new activity, saving it, and uploading it to see if that pushes any missing or pending uploads to your account.
Log out of the Strava app, then log back in.
Turn your phone off and back on again.
Make sure you're in an area with good data coverage or, even better, connect to WiFi. Navigate to You > Activities and pull down slightly on the feed, as if refreshing. Your phone may show "Pending Uploads." Tap Retry to prompt your phone to attempt the sync again.
If this doesn't work, the activity may be corrupted and unable to be uploaded. In this case, tap Pending Upload to navigate to the "Unsynced Activities" page, then tap Delete to remove the failed upload.