If you have lost your RDS CAL license key, you will need to contact Microsoft support for assistance in recovering it. You may be required to provide proof of purchase, such as an invoice, to verify your ownership of the license. It's important to keep a copy of the license key pack ID, as this can facilitate communications with Microsoft regarding your RDS CALs.
You can find more information on how to migrate or recover your RDS CALs in the documentation provided by Microsoft.
References:
- Migrate your Remote Desktop Services Client Access Licenses (RDS CALs)
- License Remote Desktop Services with Client Access Licenses (CALs)
- Find and use product keys for volume licensing
- OEM license and billing FAQ for Azure Local
- Activate Windows Terminal Server and Remote Desktop Service (RDS) without a product key