Ok another day of bug fixing adverts.
Ive followed this tutorial and have added this
Yourll need to make your blueprints a c++ By going to tools>new c++ class, I clicked none.
let it build which gives you a source file which is here
D:\Unreal Projects{Yourproject}\Source{Yourproject} Is where the build.cs is.
and
D:\Unreal Projects{Yourproject}\Source Is where your target.cs is.
Both will have your project name infront of them.
Uncommented this in build.cs
PrivateDependencyModuleNames.Add(“OnlineSubsystem”);
Add these lines in target.cs
if (Target.Platform == UnrealTargetPlatform.Android)
{
ExtraModuleNames.Add(“OnlineSubsystemGooglePlay”);
ExtraModuleNames.Add(“OnlineSubsystem”);
}
This gave me this error.

I found this is because in my android studio I was missing alot of dependencys for google.
Although apparently unreal uses cmake 3.10.2.4988404
I also have 3.22.1 and 3.31.6 installed as well.
and I added these in the sdk tools section. (Not sure all of them are needed but 
Im shooting in the dark here.
google play apk expansion library
google play instant development sdk
google play licensing library
google play play services
google play repository
google play usb driver
google play web driver
After installing, I did have to manually ask for update in android studio in the bottom left cog, It updated a bunch of things.
Im going to make sure the path cmake is correct for unreal.
Delete intermediates, binaries and saved. folders and repackage the game.
Now Im going to test and see what I get.
Update:
I had significantly larger issues, it seems.
Visual Studio needed updating several times, and is missing some tools.