I'm not sure about this but 1xbet is a reputable fiat gambling site in my country and I've used it more times than I can remember because of their fast payouts and betting options. I never had any problem with them they are also top sponsors of some European clubs so I doubt they are running Illegal business.
I don't know where are you from, but 1xbet have probably worst reputation around the world from all big bookmakers. Maybe you didn't have any issue with them, but you're lucky because it's difficult to find positive reviews about 1xbet.
And fact that they're sponsors of some football clubs and leagues doesn't makes them legit. They spend huge money for marketing to make better image about themselves. Some people will think that sponsor of Barcelona can't be scam.
BTW, some clubs ended their partnership with 1xbet after some allegations:
https://www.sportspromedia.com/news/chelsea-and-liverpool-join-spurs-in-dumping-1xbet-sponsorship/