I recently won a contest from Coinroyale and have already received a free bet of $100. Thanks icopress, inspace and Coinroyale.

After that, I made a low-risk bet with them that Katerina Siniakova would win in a tennis match yesterday.
Now I have 0.00047393 BTC in my balance and when I try to place any other bet, I get an "Invalid bet". What is the reason for this?