To create and upload an Apple push certificate to manage your iOS devices through Systems Manager, complete the 5 steps found on the Organization > MDM > Apple MDM page, also shown below.
A valid certificate generated from Apple's push certificate portal is named MDM_ Meraki Inc._Certificate.pem. If the push certificate you create is listed under a different name, the certificate will not be accepted when uploaded into Dashboard (re-naming the file will not resolve the issue).
The most common cause for this error is when the process is completed using Internet Explorer. There are a few known compatibility issues with Internet Explorer, so it is recommended you obtain the certificate using the latest version of Google Chrome or Mozilla Firefox.
Best practice is to use an Apple ID that belongs to your organization rather than a personal account, if possible. The push cert needs to be renewed every year, which requires a Dashboard admin to log into the same Apple account to generate a new token. For information on renewing a certificate, view this article.