Etsy has paused your shop's requests for the day. Shuttle has to stop until Etsy lifts the limit.
Why it happens
Etsy limits how much an app can change in one shop each day. A large run can use up that allowance before it finishes. Etsy sets this limit, so Shuttle cannot raise it or get around it.
You are most likely to hit it when:
You transfer or update a large number of products in one day.
You transfer many orders or store many reviews at the same time.
Several big runs happen on the same day.
To see if this is the cause, look for the "You've hit Etsy's API call limit" banner at the top of the Products page. Shuttle also emails you when a run stops because of the limit.
How to fix it
Wait for Etsy to lift the limit. The banner on the Products page shows roughly when that will happen.
Don't start new transfers or updates while the banner is showing. They stop at the same point.
When the limit is lifted, open Products. If the banner says "Last transfer didn't finish", click Continue to pick up where the run stopped.
If the error showed on a single product, transfer or update that product again.
To stay under the limit next time, split very large transfers across several days.
For more on how Etsy's limit works, see What is the Etsy API Call Limit?.
Still seeing it?
Contact support if the banner is gone but new transfers still stop with this error, or if a whole day has passed and the limit has not lifted.