All rear brake lights work, except the lower right brake light

If the left side works the system is working, you can see in the brake light wiring diagrams below there is a connection between the left and right brake light. I would use a test light to double check if you are getting power at the white wire near the brake light bulb. Here is a guide with the brake light wiring diagrams below:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

and

https://www.2carpros.com/articles/brake-lights-not-working

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.