How do you actually get engineering to adopt Pact contract testing?

Sold Pact to leadership. Set up the broker. Wrote example consumer + provider tests. Two teams tried it, three teams politely ignored it. The teams that ignored it are exactly the ones causing cross-service breakages in staging. For anyone who's driven Pact adoption across multiple teams: what actually worked? Executive mandate? Making it a deploy gate? Pair sessions? Onboarding template? Every "how to adopt Pact" post covers the tool, not the org problem.