Outbound client certificate expired
Your service connects OUTBOUND to a bank partner's API using a client certificate the partner issued you for mTLS. At 00:00 UTC all calls to the partner start failing with TLS handshake errors; the partner's logs (they shared) say 'client certificate expired.' Your monitoring watches the partner's SERVER cert expiry and the partner's endpoint is healthy and serving. Your own public-facing leaf certs are all fine and freshly renewed. The partner integration has worked untouched for a year. How do you triage and mitigate?
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 35 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.