I just got our iOS Push Notifications working with brainCloud and would like to add a few tips to this thread.
For the less Mac-Savvy developers like me, here's what it looks like when you only have your certificate with no private key to export as a P12 file:Screen Shot 2019-06-19 at 4.02.20 PM.png
Notice the selected category is [My Certificates]. Certificates in the [Certificates] category have the P12 export option greyed out.
I am using Unity as a development platform and for some reason my device would only receive Development Push Notifications even when running in Release in Xcode. It's only after uploading to TestFlight that my Production Push Notifications started working.