No Charge or Credit

I need to apply a NO CHARGE INVOICE for my record keeping so I can go back and remember why I didn't charge them and for how long... Example.. I do not charge a dancer when they have a medical issue like a fractured foot... I want to post a NO CHARGE invoice for that month to keep a record of what I have NOT charged them, for how long and how much.. BUT / DSP will not post a NO CHARGE invoice and instead changes it to a credit. DSP then will not apply the credit to an invoice since there isn't any.... DSP then charges them a late fee for not applied credit... DSP won't split the no pay credit.. Ugh... HELP??