vCenter is licensed with a separate license key that is usually called "vCenter Stardard" while the license called "Enterprise Plus" is assigned to ESXi hosts. You need to get a vCenter license to assign to the vCSA. There is not a separate license type for vCSA versus Windows vCenter.
was your original licenses attached to an essentials pack if so then your vCenter license would not be eligible for additional ESXi Hosts. you would have to re-license it with a vCenter Standard License key.
To be honest, I only had one key and I can't go back and retrieve the licenses to look at the features. The data sheet shows VCSA under Enterprise Plus so unless somehow I am completely misremembering how I built those system this snip supports my recollection of the single Enterprise Plus license containing VCSA.
vCenter has always had its own license key, be that an essentials vcenter license or a Standard license. if you only have a single key then that would be for your ESXi hosts and NOT for vCenter.
you should be able to check your licenses in your MYVMWARE portal. if you do not know the access details speak to your vmware reseller who will be able to help you in finding out your true licensed position.
vCenter (VCSA or Windows) comes in 4 different flavors
1. vCenter Standard (the big one)
2. vCenter Foundation (max. 4(was 3 earlier) Hosts)
3. vCenter Essentials (max. 3 Hosts)
4. vCenter in Trial Mode
You ESXI Enterprise Plus licenses can only join to 1,2 and 4 of course. Not 3!
In the early days that might be technicly possible but it was always forbidden by EULA. IIRC since 5.x you cant mix Essentials stuff with Non-Essentials any more.
Also you cant buy vCenter Essentials as a standalone product like the others. vCenter Essential always comes was part of the Essentials Bundles.
So please check your vCenter license.
Thanks everyone for chiming in... I have VC Standard Licenses on order and just moving forward from here
Excellent news, and now you know where to go to get help and questions answered.
welcome to the community.