First operational issue
Operational issue will happen before or later. One of the first actions of the API consumer is to identify the root cause.
Operational monitoring
API consumers should be able to access status pr API on uptime. This should automatically be updated based on health checks running continously.
Low bar for reaching out
Provide a slack channel for your API, where API producers can inform of downtime and the actions being taken to recover operational status.
Post mortem
After any significant downtime, the API producers should supply the API consumers on a post mortem report on the root cause for the downtime and mitigating actions taken in order to reduce the likelihood of similar issues in the future.