photoshop CC plan und bought an addtional lightroom 6 license. no third activation possible

I have a photoshop CC plan und bought an addtional lightroom 6 license. I think i could activate 2 photoshop and lightroom cc on two device and use lightroom 6 (bought separately) for one or two addtional devices (I use one adobe ID for CC and added the Serial number of lightroom 6 this account) . If I try to install lightroom 6 on the third device, it refuses to active because of the 2 CC activations but I used the SN of the bought version. how to solve  this? any advice welcome