My license is in my dashboard but I can't use it.

Unfortunately, this does happen! If your Cinema 4D license is visible in your dashboard but you cannot open or use it, it's highly likely that you're logged into your account on two different devices. You can try to log out on both devices and log back into the account on your preferred machine.

Alternatively, if you're logged in on two different machines, Device 1 and Device 2, but would like to log into Device 2, the best workaround is go to Device 1 and select "quit and free license". Then, go on Device 2 and try to use your license.