glass shower screen for shower tray

it has either been fitted incorrectly or the seal is missing.

If it's bath shower screen and if you can open it out/in that definitely there should be gasket and basically if on wall bracket hold the glass above the edge of the bath or shower tray about a couple of mm it's mean that there is a gasket missing but if the gap is no bigger than 1mm for stiff screen can be given silicone instead if there is no choice.

I’d recommend looking for a seal for the bottom of the screen if there isn’t one fitted or hasn’t been fitted when installed or there is a Mis measurement

If I'm understanding this correctly it sounds like a walk in shower and the length is a little short as it's a glass screen and not a cubicle? If that's the case you can retro fit a flipper panel but you will need to check the height and width of the glass. Some work with hinges/gaskets that bolt onto the existing screen

If it is a wetroom type shower screen then unfortunately they are predrilled to accept a fixed or return panel. It would be difficult to find a company that would drill the glass after it has been installed. If the screen is part of a shower enclosure then as previously mentioned it may have been installed incorrectly.

If shower screen is short you can purchase extended profiles