Carlos Sainz did not accept the fine imposed by the FIA at all: here are his words.
Carlos Sainz didn’t take it well, if that’s the right way to put it. The Spaniard was fined €10,000 for being five seconds late to the national anthem ceremony: no negligence on the part of number 55, but rather an intestinal problem that forced him to rush to the bathroom.

Jon Noble from The Race asked the Spaniard for his opinion: “You had quite an expensive toilet break before the last race. You were fined for missing the drivers’ parade. Were you surprised that despite the reason, you still got fined?”
Here’s Carlos Sainz’s response: “I think I’m the biggest supporter of punctuality and being—in a way—a gentleman, being punctual to things, especially to the national anthem, with all the authorities there. So I was the first one to raise my hand and say, ‘I’m late. I’m sorry for that.’
At the same time, I was five seconds late. And to be five seconds late and have to pay €10,000 or whatever the fine is, for me, it’s absurd that we have to pay these fines.
But yeah, I don’t know if I’m going to get another fine for saying this, but… ‘shit happens.’ It’s the way it goes sometimes. I mean, €10,000—you guys know well what €10,000 is.
And for five seconds, it’s disappointing. I hope, as I’ve always said, that someone tells me where this €10,000 goes. And if they say, ‘OK, at least it went to a good cause,’ then I’ll be happy to know where it goes.”