Steve Lewis wrote:

If you are challenged as to whether you touched-in, refer them to the bus
CCTV, as one of the cameras (if functioning correctly) will have recorded
your attempt to touch-in.

That would be the pragmatic thing to do, but it doesn't really address the
fundamental issue, because the CCTV is just part of the adversary's system.
For a start, you cannot be sure the CCTV is operational.

What you need to do is to film it yourself.

Or get a receipt.