Client asked for a proposal and you have never sent one
Do not panic and do not promise to send it tonight. Reply that you will send a written proposal by a specific day, ideally within 48 hours. A deadline you set beats a rushed document every time.
Write down everything the client said they want, in their words. Most first proposals fail because the freelancer guessed at the problem instead of repeating it back.
Structure beats polish. One page each of problem, solution, deliverables, timeline, and price will beat a pretty ten pager that says nothing. Length never closed a deal that clarity lost.
Name one fixed price alongside two alternatives: a smaller option and a larger one. Three options turn a yes-or-no decision into a which-one decision.
Send it as a link, not an attachment. Then follow up once after three days with one specific question, not a just-checking-in note.