It is said that the amount can vary depending on your activity and VIP level. In the casino that I am currently playing, they also have a monthly bonus and its also based on the VIP level and wager, not the activity. Activity could mean by login in, chatting, depositing but I don't know if wagering is included with it in their own terms. ~
Activity means deposits and wagering, some casino also includes profit/lose amount in it. Activity doesn't mean what you have said above. Almost every casino gives monthly bonus to their users now. This isn't a new addition in Bitsler. They had sent monthly bonus three times in the last year. But they didn't continue it. Anyway, now it seems like Bitsler will give monthly bonus in each month.