Make room for the other version
Ask what the other person understood before assuming that you are arguing about the same facts. For a message about how to agree on a holiday parenting schedule, use this factual base: state the child's schedule, health, school, expense, or behavior and distinguish observation from interpretation.
Correct the record precisely
Correct only what you can support, acknowledge any real impact, and propose a practical way to prevent repetition. Propose a child-focused plan, a response date, and the documented route for unresolved decisions. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Agree on a testable next step
Do not use the child as messenger, trade access for agreement, or criticize the other parent to the child. Follow custody orders and use safeguarding, legal, medical, or emergency support for risk to a child. Do not recruit an audience, publish private evidence, or turn a misunderstanding into a campaign about character.