May I be bold enough to inquire why you bought Lr 6 when you know you can get Lr CC as part of the Photography bundle at no extra cost?
You may have to set up a second account. This is from someone else who had a similar problem:
"The workaround, actually, is simple: you need separate Adobe accounts for your CC and standalone Lightroom licenses. It's easy enough to register a second account. The only complication is that if you have already purchased a standalone license (upgrade or new) while logged into your existing Adobe account, you will need the assistance of a customer support rep to move that license and, in the case of an upgrade license, the license for your qualifying software to the second account.
Unfortunately, the first-line support rep I spoke to didn't know what to do. Nor did the one to whom he escalated my inquiry. The third rep figured it out with a few nudges from me—I had already guessed the workaround, but was hoping there was a clean fix—and he moved my standalone license to a second Adobe account. I'm now running LR on three machines: two under a CC license and the third under a perpetual license."
Well, it's similar to the reason I own a house rather than rent it. Rent is perpetual loss of capital. Buying allows you to stop paying when it is payed for.
Thanks John. I figured it was something weird like that but was hoping for simpler.