“On Android, you will need to create a key to sign the .apk, and give some information to our build tools with a file called SigningConfig.xml. This file exists in the installed Engine directory (Engine/Build/Android/Java). If you edit this file, it will apply to all your projects. However, you can copy this file to your project’s Build/Android directory (no Java directory), and it will be used for just that project. Directions for how to generate the key and fill out the file are found in the file itself.” Packaging Unreal Engine Projects | Unreal Engine Documentation
My problem was I have to put double slashes in the path to my keystore file.
Create your apk digital key:
“On Android, you will need to create a key to sign the .apk, and give some information to our build tools with a file called SigningConfig.xml. This file exists in the installed Engine directory (Engine/Build/Android/Java). If you edit this file, it will apply to all your projects. However, you can copy this file to your project’s Build/Android directory (no Java directory), and it will be used for just that project. Directions for how to generate the key and fill out the file are found in the file itself.” Packaging Unreal Engine Projects | Unreal Engine Documentation