When sending a letter to a client or customer requesting payment, it's essential to clearly communicate your point while maintaining a positive, professional tone. The worst thing you can do is send a first or second request payment letter that is so negative the client feels attacked. If the tone is too harsh, the client may feel there is no point in trying to continue a relationship with your business. When that happens, there's a risk the client will decide not to pay the bill since he or she is not concerned with preserving the relationship.