If a server error appears while you are working in the app admin, check the following causes in order.
Eligible items, collections, and product tags for a rule are each limited to a maximum of 50 per rule. Setting 51 or more and saving can cause a server error. Reduce the count to 50 or fewer and save again.
A server error can also occur due to an outage on Shopify's side. Check Shopify Status to see whether Shopify is experiencing an issue. If the cause is an outage on Shopify's side, wait until it is resolved.
If the problem persists after checking the above, contact us through the inquiry form. For our investigation, please let us know the screen where the error appeared, what you were doing, and when it occurred.