The demand brought a dispute to light. Change the next question.

The customer finally replies with details
Suppose a customer answers your demand by identifying a disputed extra-work charge and attaching an earlier email. Until now, the account appeared to be a simple failure to pay. The new response needs review before another unchanged demand goes out.
Read what is actually contested. A late objection is not automatically correct, but treating every objection as an excuse can prevent you from understanding the account you are trying to recover.
Match the response to the account
Identify the invoices, quantities or rates mentioned. Compare them with the demand and supporting documents. Ask for clarification if the response uses a broad label such as “defects” without identifying the work or amount involved.
Keep the undisputed and disputed components distinguishable in the working file. Do not assume that your own view of the split establishes an immediate legal entitlement to a particular payment.
Return to the agreement and the evidence
business.gov.au advises reviewing payment conditions and debt recovery provisions when an invoice remains unpaid. Read those terms alongside the new response and any relevant instructions or approvals.
If part of the agreement was verbal, identify the available records of what was discussed. Do not create a retrospective approval to close a gap. Explain uncertainty to the adviser who assesses the dispute.
Source: business.gov.au: What to do when you haven't been paid
Answer the specific point first
If the customer has identified a genuine arithmetic or allocation error, correct it and show the revised reconciliation. If the issue concerns work or authority, identify the documents that address that question and the information still needed.
Avoid sending the entire history without a concise explanation. A focused response is easier to assess than another large attachment bundle with no connection to the objection.
Keep formal deadlines separate
Check any actual court, statutory or contractual notice with an appropriate adviser. A discussion about the invoice should not lead you to assume that a formal response period has stopped.
Likewise, do not claim your own requested response date has the same effect as a statutory deadline. Ask about the available process before threatening a particular consequence for the customer's reply.
Choose the route that now fits
The next step may be clarification, negotiation, mediation or legal advice, depending on the documents and circumstances. Record why the approach changed so everyone handling the account follows the same position.
Use Report a Dispute below if the response has revealed a substantive disagreement that CRP can help organise. Bring the demand, reply and current reconciliation. The useful outcome is a better-defined problem, not another reminder that ignores the information you just received.