Once you have successfully prepared and sent the demand letter, there are a few possible outcomes:
The demand is met. The other party accepts your demands and provides payment.
The other party makes a counteroffer. The other party is willing to provide partial payment. You do not have to accept the counteroffer and you may present a counteroffer of your own.
The demand is rejected. The other party refuses to pay or provide services. In this case, you may have no other recourse but to file a lawsuit.