Question:
When a customer pays their invoice online is there a way to tie a customer to a DNN account?

Answer:
Yes, when a customer pays their invoice online their customer and payment record is tied to their dnn account. When the user makes payment and they are not a member the payment registration module will create a new account for the user. If the user makes payment and they are already have a dnn account then the module will use their existing dnn account and associate the new information (customer and payment) they enter with their existing dnn account.