The issue is related to sales channel connection in Webgility Online

1). Go to Settings> Connection

2). Click on Edit Connection and select Update Credentials

3). Click on Continue to update the credentials and test the connection

If the error still comes please check the sales channel permissions and get this done from the sales channel backend to allow full permission for the Webgility application and try again to test the connection in Webgility

Note: If the error persists please contact Webgility support.