To enter your ESXi host serial number, perform the follow steps:
- Go to the Home screen of your vSphere client and click on the server in your inventory you wish to apply the license to
- Click on the Configuration tab on the right hand side
- On the left side,click on Licensed features
- Click Edit
- Choose Assign new key to this host
Now you can enter in your license key and confirm all of the open screens. From here you will have a fully licensed ESXi host.