The maximum stake in Bet365 varies depending on the sport, event, market, and the type of bet that you want to place. Bet365 has established maximum payout limits for each sport, which can limit the maximum stake that you can place on a specific market.
However, winning too often will see your account with bet365 restricted. This is why bookmakers don't like professional gamblers who consistently win. It is bad for business, and bookmakers are out to make money, not lose them.