I checked the body to see if a call worked. The status line already said it. The number is the verdict and the body is only the payload, so read the number first.
About 1 min of reading
Read the status class of a few calls and blame the right side.
A good call returns 200. The class is success.
Before you run it, say out loud what it will print. Then open the answer.
A path that does not exist returns 404. The class is your fault, fix the path.
Before you run it, say out loud what it will print. Then open the answer.
A malformed body returns 400. Still your fault, the request was wrong.
Before you run it, say out loud what it will print. Then open the answer.
2 success, 3 redirect, 4 your fault, 5 server fault. That one digit tells you who to blame. A 4xx you fix in the request, a 5xx you report to the service. Reading the class is faster than reading the phrase.
Some services return 200 with an error in the body. That is a design smell: the status lies. Trust the status when the service is honest, and when it is not, that dishonesty is a thing to report, not to work around silently.
200 OK
201 Created2xx means it worked. 200 is a plain success, 201 means a new resource was made. Both are green.
400 Bad Request
404 Not Found4xx means your request was the problem. 400 is a malformed body, 404 is a path that does not exist. The fault is on your side.
500 Internal Server Error
503 Unavailable5xx means the server broke. Your request may be perfect. A 500 is the server's own crash, not your typo.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.