If your charger is charging slower than expected, check the following things
Is the energy mode Solar Only or Smart Solar? Try switching to Fast (Overview > Energy mode) and see if that helps.
Fast mode
Solar balancing
If the charger is in Fast and still charging slowly, maybe you are using a lot of power elsewhere in your home and load balancing is lowering the charging power to stay within the main fuse value set for your location.
Also try switching off Peak Shaving (Overview > Energy mode)
Peak Shaving
Is it a newly installed charger? Ask your installer at which maximum power they installed it.
Did you switch cars recently? A new car may charge slower, for instance if it charges at a lower A or with fewer phases.
If:
The charger is in Fast
You are not using a lot of power elsewhere in your home
The charger is not new
You are charging the same car as always
Check if the kWh's per session in the app are (about) the same as your car says. If there's a very large difference, maybe the meter inside your charger is damaged.
Metering problems
If the car really is charging a lot slower, maybe there is something wrong with the installation or the charger. Contact your installer.