I'm not a tax accountant so I couldn't say for certain. But if this is an additional payment for a seat reservation on an international flight, I would assume i

I'm not a tax accountant so I couldn't say for certain. But if this is an additional payment for a seat reservation on an international flight, I would assume it falls into the same category of "international travel", which I believe is zero-VAT across EU. If it was something not directly related to the travel aspect itself, e.g. pre booking an inflight meal or lounge access, I would expect VAT to apply. Or a domestic flight within France, of course.