By any chance did you make this purchase on a fresh character on a fresh server? If this is the case, you will need to unlock your Legacy, and then you should be able to create a Chiss on this server. Note that the requirements to unlock your Legacy are now to complete your Origin world, rather than Chapter 1.
If you're on a server with an existing Legacy, is the unlock showing on your Legacy page?
So the Chiss unlock is only valid for the server I currently have an existing legacy on, or I just need to buy and unlock it with a legacy character and it will be available everywhere?
I ask because my level 45 (highest level) is on one server, but my friends are playing now (since it's gone free to play) on a different server. So can I unlock Chiss with my level 45 and have it available on the other server, or do I have to get a legacy on the new server and unlock Chiss there? Or after I buy it on any server, it'll be available on any other server where I activate legacy (by completing the Origin world)