First, find out what the client doesn’t understand
The invoice says “Revisions—Package B,” and the client asks what they are paying for. You know it means additional presentation versions. But the document may be read by someone in finance who wasn’t involved in the project. Your team’s everyday shorthand tells that person very little.
Ask what is unclear. Does the client not recognize the work, question the hours, or wonder why the amount differs from the quote? Each question needs a different answer. Sending the whole old thread simply hands the search over to them.
Connect the item to the agreement and delivered work
Take a presentation for which the client ordered two extra versions for the sales team. Find the message agreeing to them and the links to the delivered files. Your reply should identify the output and its connection to the price, rather than defend how much effort the whole project took.
Instead of “we already discussed this,” try the message below. Use the dates, descriptions, and links that you can actually support for your project.
Select the text, copy it into an email and fill in the details in square brackets.
If the supporting agreement is missing, wording won’t fix it
If you cannot find approval of a change, don’t cover the gap with a more confident email. Say you will check what was agreed, and speak to the person who discussed it with the client. If you find incorrect quantities or another mistake on your side, name the error and agree how to put it right.
You may also discover that the client recognizes the work but disagrees about what was ordered. That is no longer a description problem. The people who agreed the scope need to revisit the conversation; sending the same attachment again will not settle it.
Next time, describe the output for someone outside the project
Compare “Package B” with “two additional presentation versions for the sales team.” The clearer description doesn’t need a whole paragraph, but it tells the reader what they received. For an ongoing service, the relevant period and scope can provide the same clarity.
Keep the resolved question and your reply with the project. If the same question keeps coming back, improve future item descriptions. Don’t silently replace a document you have already sent; the recipient needs to know which invoice your explanation refers to.