Please accept our most sincere apologies for this inconvenience.
Shopify upgraded API, and Ryviu might get trouble when accessing your store so please reconnect your store with Ryviu follow exactly these steps below to update Ryviu app to fix this issue:
Step 1: Login your Shopify admin > Apps, click on Ryviu - Product Reviews to log in your Ryviu account
Step 2: Update Ryviu app: Open this link below, click UPDATE APP button to fix this issue.
You are done.
Thank in advance,