Clarify the agreement that existed
Identify the promise, policy, schedule, ownership, or shared understanding that applies before assigning blame. For a message about how to apologize for breaking a building rule, use this factual base: state the date, place, property, noise, pet, or shared-space impact without arguing about the neighbor's character.
Resolve the next dependency
State what is complete, what remains disputed, and which action would move the situation forward. Offer cleanup, replacement, access, a schedule, or another practical remedy you can complete. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Document without threatening
Do not threaten, shame the neighbor publicly, or involve the whole building in a private issue. Use property management, local authorities, or emergency services for genuine danger rather than confronting someone unsafely. Keep a factual record and describe only remedies you are entitled and prepared to use.