This is a random bonus offered to players even without having o send money to their betting accounts. It could be either a reward for loyalty or a welcome carrot. Either way, the player gets to benefit because they can use it to play various games in the casino and get tangible wins.
One of the smallest and the only land-locked countries in Europe, Luxembourg, does not have any specific laws when it comes to mobile online gambling. Online gambling is illegal in this country, but only for domestic gambling websites. Players are free to play on foreign websites, which helped the popularity of mobile online gambling.