X_NOTIFY_FANOUT_TOO_WIDE
Means
the audience is larger than one run may fan out to
Typical cause
the resolved audience passed maxRecipients (default 500). One step per recipient is what makes a provider blip re-send one address rather than all of them, and a step is a durable row — so there is a width past which this is the wrong shape entirely. Refused with both numbers rather than degraded silently
Fix
deliver through a bulkChannel() on notifier("<name>"), which sends one payload for every recipient, or page the audience with backfill() from @ultimat3/jobs