I saw this post and thought I would offer assistance. In the past you had to use Cisco's AIR-CHNL-ADAPTER brackets and mount the Meraki Adapters to it. Meraki has its own clips that work like the AIR-CHNL-ADAPTER brackets, but look like the normal adapters that are shipped with APs. The difference is the clips are deeper. I know it's hard to describe but this part number: MA-MNT-CLG-1 includes a pair of deep drop ceiling clips for channel rail as well as spare T-Rail adapter clips which supports both recessed T-Rail and flush T-Rail. The deep drop ceiling clip works well with "Armstrong Silhouette" and similar ceiling grids which are found in newer building designs, its basically a channel rail (not a T-Rail). This kit is compatible with all Meraki MR access points and MV21 & MV71 security cameras.
Everyone knows the T-Rail here's a good picture of it:
Meraki APs Come with an adapter for this by default. but If you want to mount on
the channel rails pictured above, you will want to order MA-MNT-CLG-1
separately when ordering your APs.
Good luck out there all!!!
HTH!