I know this has been raised in other threads but I’m not sure I understand where the sealant goes correctly. Basically we have a leak between the glass and the chrome trim. I can see there is an outer bead of silicone on the outside of the glass screen and trim right at the bottom along the shower tray. It also looks like there is sealant between the trim and the wall. These elements sound correct, so how do we stop it, I don’t want to get the plumber round until I understand how it should be done as it sounds like these are messed up even more by return visits! The leak point is where the arrow is.

The rule seems to be only mastic the outside.  In this case, just run the mastic up 50mm vertically between the glass and the profile and any water in the profile should drain back out into the tray.