If you have verified there are not authentication issues related to your EBSCO scope and are still unable to retrieve any results, it could be that your subscription package has changed and that one of the databases you previously subscribed to is no longer being subscribed to. The way the EBSCO API works, it fails if you pass it a database that you do not subscribe to.
When there is no longer access to even one of the databases listed in the Ebsco scope configuration (whether blended or not), the entire scope will break.
- Find your list of configured databases
For regular Primo, go to the Back Office > Mapping Tables > Deep Search Parameter Plugins > Param name: DB for Plugin: Ebsco
For Primo VE, go to Discovery > Search Profiles > Other Indexes (tab) > Ebsco > Databases
- Look at your configuration and test it directly with the Ebsco API.
Ex Libris provides instructions on how to do this here: https://knowledge.exlibrisgroup.com/Primo/Knowledge_Articles/How_to_test_EBSCO_API_outside_of_Primo