How to make available iOS app to different client's MDM We have developed and Enterprise iOS app and we want to deliver this app to different clients. 

Each client have thousands of employees and they will manage themselves the deployment of the app in their employee's devices.

Want we want to do is to deliver the iOS App (make available) to our clients MDM's. We have a Cisco meraki as MDM.

Whats the correct way to go?
When it comes to AirWatch, I as MDM admin have the option to upload a file, containing the application. So you would have to deliver your IPA file to your client. Now, it's just me guessing, but I would believe every MDM that allows to publish internal apps has this option. 

Another option, and I guess it would be the preferred one, is managing your app as B2B app in the VPP program. Here is a write-up I found of how the process works.

http://www.techrepublic.com/blog/apple-in-the-enterprise/how-to-purchase-and-deploy-custom-b2b-apps-through-apples-vpp/