Android Unity 64 bits Google Play

We are trying to upload a mixed (native, and Unity as a library) app to Google Play Store, but it doesn't let us publish it. It says that the app is built only for 32bit and that we are missing some 64bit libraries. When we export the project we have the armv7, arm64 and x86 check boxes checked, but I think that we are missing is x86_64, as Google specifies here https://developer.android.com/distribute/best-practices/develop/64-bit#64-bit-libraries.
We have not found any option to include it in the exported project.

Hope you can help us