Cash is NOT allowed to be placed as part of a bet or into a pot.
Cash may not be exchanged between players because money is owed.
Players are allowed to play "behind" for any amount for which they choose to buy-in( subject to buy-in limits) as long as the amount is announced prior to the hand starting.( verbal buy-ins are binding).
Any amount owed to the pot or player will be placed after the chip runner has returned with the chips.