Second attempt [1]. This increases the threshold so:
- It's a more substantial amount of money lost (£16).
- It's 10% of the minimum free allowance for a service.
- It's greater than the threshold we have for TV numbers (500).
Having a higher threshold for this alert will help prevent wasted
effort investigating more negligible failures, and reduces the
ambiguity of whether we should take action: we should.
[1]: https://github.com/alphagov/notifications-api/pull/3221
bd45d788c0