I have a bunch of Poly E550 phones I bought from Ring Central and I purchased the Poly Expansion module as well. Unfortnately, the expansion module doesn't really work because you can only add up to 48 total lines through Ring Central, although the module can include many more lines, up to like 100 or something much more.
It is connecting just find with my E550 but because it's not on Ring Central as an expansion module option, it's not allowing me to use the full potential of the expansion module. Basically, the system is thinking I don't have it and it's showing phone numbers on the expansion module but only up to line 48 because I think this is the maximum allowed on the E550 by itself. Let me know if I can expand anything further. Thank you!