Hi Tessa,
Good to know you are able to receive Beam’s output in Capture by broadcasting. This is essentially what happens when you specify the “IP address + 255 as the last digit!”. Broadcasting means the Art-Net packets will be received by every IP address within the matching subnet, which can be handy in some cases, but it is not ideal as a default scenario, as it can impair the performance of your network (and in this case possibly result in a slightly less smooth visualisation), so I would still recommend trying to make it work by unicasting (sending Art-Net to a single specific address).
The reason why broadcasting always works and, on the other hand, when unicasting, the order in which Capture and Beam (or any two Art-Net applications) are started matters, is because both applications bind to the same default Art-Net port (6454) and try to receive the packets sent to that port. However, only the application which was started first and bound to that port first will receive the (unicasted) packets. So, if you start Beam before Capture, the latter will never receive Art-Net packets sent by Beam, as Beam itself is receiving and discarding them.
Simply quitting both programs, then restarting them in the right order is usually already enough, if not (in case the quitted application doesn’t release the bound port), restarting the OS and repeating should fix the issue.
As far as the address itself goes: when you mention localhost - did you specifically try to write localhost in the Art-Net output address field (that will not work) or have you tried the 127.0.0.1 loopback address? Instead of 127.0.0.1 you could also try 0.0.0.0, though the former should already work, provided the programs were started in the right order.
It would be much appreciated if you could try this and report back if it works. When following the steps above, we have so far always managed to get it to work, so it would be valuable to know if there is something else at play.
Still, we are aware this process could be user-friendlier and hope to offer a better way of connecting to Capture in the future.
As far as getting the second universe to work, this is something you need to specifically select and assign to an internal Capture universe:
If you map it to Universe B / 2.1-512, you will be able to patch fixtures controlled by Beam’s universe 2 by specifying addresses as B.x (where x is the DMX address):
Hope this helps!