If you are still renting Serum, please make sure that you are signed into the Splice desktop client with an account that has a Serum plan active before you open up your DAW to load Serum. While you are on the Rent-to-Own plan, the client needs to verify the Serum plugin once every few days.
In order to resolve this issue, please follow these troubleshooting steps in exact order:
Close out of Splice
Close your DAW
Relaunch Splice and log into the account with the active Serum plan
Open your DAW and launch the plug-in
If you are still having issues, please again close your DAW and reinstall Serum directly from the Splice app in the "Apps & Tools" section.
We also recommend you reinstall the Splice app. You can get the latest install here: https://splice.com/download
If you've fully paid off your Serum Rent-to-Own subscription and are being prompted for a serial number, your serial number will be shown here: https://splice.com/plugins/your-plugins