This came up on the Gravy alerts:

2025-09-09T14:58:54+00:00 [INFO] (RawData) Create payment response {"type":"error","code":"bad_request","status":400,"message":"Request failed validation","details":[{"location":"body","pointer":"/buyer/billing_details/last_name","message":"String should have at least 1 character","type":"string_too_short"}]}
2025-09-09T14:58:54+00:00 [ALERT] ALERT: Gravy error threshold exceeded for error code '400'. Occurred 15 times in 30 minutes (threshold: 15)

Failmail subject with example:
FAILMAIL - ALERT: payments1007 (gravy) SmashPig-Gravy::gravy::235447353:235447353.3