When a sync fails
A failed sync leaves the previously synced data in place. Nothing is lost while you work out the cause.
Read the failure first
Open the source and read the most recent run. The failure names which stage stopped and what the source system returned, which is usually enough to tell the three common causes apart.
Expired authorisation
The most common cause. The account that authorised the connection changed its password, lost a permission, or left the company. Reauthorise the connection with an account that will not change.
Rate limits
Large sources can exceed what the source system allows. These recover on their own; the next scheduled run picks up where the last one stopped.
An outage at the source
If the source system is down, the sync will keep failing until it returns. Check the source system's own status page, then ours at our status page.
If none of these fit, contact support with the run identifier from the failed run.