A teammate rejects your suggestion twice. It is easy to conclude that they are being difficult. That conclusion may feel explanatory, but it does not tell you what would help the work move forward.
Try describing the observable obstacle instead: ‘We have not agreed on a format.’ Then identify the information that could change your next step. Do they need a different level of detail? Are they working with a constraint you have not seen? Do they disagree with the goal itself?
A useful question is: ‘What would the format need to include for it to work for you?’ This invites a criterion rather than another exchange of preferences.
Sometimes the answer will confirm a real disagreement. You do not have to pretend everyone shares the same intention or accept unreasonable behaviour. The point is to resolve the actionable uncertainty before treating your first explanation as settled.
If the conversation remains unproductive, state the decision process: ‘We have two options and different preferences. Who should make the final choice?’
A specific question gives you information you can use. A judgment about someone’s character may only give the next message a sharper tone. Start with the obstacle you can name and the answer you need.