I am European and live in Europe but I've always been paid in USD and my salary is negotiated in USD, so I am not sure what parent means or why does currency matter.
First clients were based in the US. So it started from there.
Then I wanted to use a reserve currency[1] and I happen to have strong opinions on currencies, policies (FED, ECB, etc.), so I opted for the safest bet in the long run.
Also, the question specifically says "in €, otherwise specify" (edit: ok, I see it was added later).
It's weird that you are paid in USD in Europe, isn't it? How comes?