Write from facts rather than momentum
Pause long enough to remove accusations, assumptions, and details that belong to someone else. For a message about how to ask a collaborator for proper credit, use this factual base: identify the brief, deliverable, rights, fee, revision history, and contract term that applies.
Offer a proportionate next step
Match the size of the request to the relationship and to what the recipient can reasonably decide now. State what you can deliver next, what approval or payment is required, and when the offer expires. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Protect privacy on both sides
Do not release rights or final files beyond the agreement, and do not shame a client publicly. Use platform support, legal advice, or a formal takedown process for fraud, infringement, threats, or identity misuse. Use the most private legitimate channel available and do not share the exchange to recruit support or pressure.