The Maximum allowed booking value will show the maximum value of bookings allowed for your account at the selected Bidding level.
*Maximum allowed booking value = the possible booking amount
*Available commission = the maximum commission for which you have credit in your account
Your Google Ad will not be shown if the Guest enters dates that would generate a booking of higher value than this.
If this is too low, you can raise it by adding funds to your account. There must always be enough funds in your account to cover the Google commission at the time the Ad is shown.