Is your API actually up?
Paste a URL. In a couple of seconds you get the status code, the response time, how long the certificate has left, and what DNS says.
No account, no card. We check the status, the response time, the certificate and the DNS.
A single check tells you less than you think
Everything above is a snapshot. The failures that actually cost you money are the ones that happen while you are not looking.
The certificate you forgot
It is valid today. In 47 days it is not, and nobody gets a reminder except your customers.
The slow slide
200 ms today, 900 ms next month, 3 s by spring. No single day looks like an incident.
The 200 that lies
Status 200, and a field in the JSON quietly changed type. Your clients break; your monitoring says everything is fine.
The webhook that stopped
Stripe stopped calling you. Payments still go through. Your database never hears about them.