When adding to protection a VM agentlessly, the task fails with "Current license or ESXi version prohibits execution of the requested operation".
If a license was already configured in the VMware environment but it was unmounted for any reason, we can experience symptoms like:
vSphere Storage APIs – Data Protection (formerly known as VMware vStorage APIs for Data Protection) are required by the software to perform agentless backups.
Data Protection APIs are included with all licensed vSphere editions except the Free editions.
In order to review the License Keys of ESXi Hosts from the vSphere Client please follow the steps in the following VMware article.
Any license different from the free version is required to access the required Storage APIs - Data Protection.
Agent-based backups can be used if a non-Free license is not available.