Here are steps you can do to fix the issue:
1. You can access your WebplatformConfig key in the Customization Manager and open up your entry.
2. Click on the API key, and there are three dots to the right. That will bring in a new API key.
3. After that, you will need to restart your IIS. If you are hosted by OCLC, Contact OCLC Support
4. We will restart IIS.
If you are self-hosted, you want to contact your Web Server Administrator to restart IIS.
If you continue to have issues, we will want your ILLiad client log and ILLiadWebPlatform Log if you are self-hosted. If you are hosted by us, we will want your ILLiad client log.