You might be able to lift the grey plastic bit out. It may be the case that it is clogged by hair.
There are acid based products that will dissolve any hair pretty quickly, but they are now semi-restricted items. I can buy OneShot from my local store, but only because I have a trade account. I would however recommend that you explore other options first. I you use acids and they do not clear the obstruction, you will have acid sitting in pipe would could harm a plumber if one is required.
There may be a dip tube in the middle, see if anything will pull up and out. This would then reveal the outlet. If not then a wet vac would be my next choice, see if you can pull the blockage back up and out the pipework. Failing that, then you will need to access the outgoing pipework at a suitable point and look at cutting into it to clean it out.
Avoid chemicals, they are dangerous, especially if they dont work and someone then need to used other means to clear the pipe.
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