[tener]

So... Meta has been fined for illegally using customer data, which they value at hundreds of euro per year. Can the customers sue for back payment?

[colonwqbang]

This theory would be interesting to see tried in court. Is there an obvious legal argument against it?

[throw_a_grenade]

Nothing in GDPR gives you legal basis for that (the penalties under GDPR are paid to the state). But there isn't anything that prevents you to sue them either, so you just need to find another legal basis (like, to prove a damage) and convince the civil court. Civil courts have famously low standard (preponderance of evidence), so it doesn't sound easy, but it doesn't sound hard either.