Hi The Manifest only describe the list of the file that is in the project.
And the ApiKey is the key associated with the mobile application.
So this is not what you are looking for.
For the class.dex this is a compressed format so I never understood how this transformed in .txt could deliver some text…
But some people were able to do it so.
It could be much easier to deliver the KEY by pm but I was not able to find somebody who was ready to do it. I keep hope 
Regards