Disclaimer: This procedure changes the license state of a vSAN Witness Appliance and may temporarily affect the witness configuration in a stretched cluster or 2-node cluster. Make sure you have a maintenance window and verify the health/state of the cluster before you begin.
Broadcom/VMware documents that the vSAN Witness Appliance includes an embedded vSphere license and does not require a separate purchased license for the virtual appliance itself. There is also an official KB for cases where the witness shows up with an expired or evaluation license in vCenter after a major upgrade. But if the original embedded key has actually been overwritten, the normal disconnect/reconnect workaround may not be enough.
I recently ran into a situation where the embedded license on a vSAN Witness Appliance had been overwritten with a regular ESXi license key.
The witness appliance is supposed to use its built-in embedded license, so this needed to be reverted.
If the witness is still part of a vSAN stretched cluster or 2-node configuration, remove it from that configuration first.
Below is the procedure that worked for me.