Hi,
I contacted unity support email a few days ago now with this and no response…
I work on 2 different computers, both using the same seat as is allowed.
I recently bought a new PC, so I wish to begin using the new PC instead of the old one for that machine assigned to the seat.
After installing unity on the new machine, pasting in my license for Unity Plus gives the error message: “Serial has reached the maximum number of activations. Disable existing activations to reuse this serial key… Please contact support@unity3d.com for more information.”
There is a link in the error, taking me here: https://store.unity3d.com/account/licenses#activations_21435067
Where I see nothing which can be used to disabled exaisting activations. It looks like:
I follow the “Manage subscriptions from the new online store” link, but there is nothing there either.
I have tried removing the seat allocation from myself and then reallocating the seat, but I get the same problem.
I just want to activate plus license I have for this machine, as I wont be using the old machine any longer… How am I meant to do this?? 3 days with no response on email now…

I am having the exact same issue. I tried removing my own seat and re-adding it but it made no difference.
– BobBobson108Same exact issue here. I didn't login into unity for a couple of weeks and when i relogged it gave me that error message :/ I tried to remove and re-add seat but it didn't solve the problem.
– Ser_MersadionAnyone ever figure this out?
– Thorny2000I did email support@unity3d.com too and they solved the issue quite quickly.
– Ser_Mersadion