2xx - "Yup, that worked, probably"
200 is usually a good thing.
400 Bad Request - “I haven’t got a clue what you are asking”.
The way you formed the API URL is likely to be wrong, double check !
401 Unauthorized - "I don’t know who you are, you need to authenticate yourself"
You will need to do some form of authentication … check the API documentation
403 Forbidden - “I know who you are, but I am not letting you at that”/
In this case you have probably authenticated OK, but you don’t have permission to do what you asked. Might be worth looking at SCOPEs you have asked for ? Also check on the method (PUT, GET etc) here as well.
404 Not Found - “I can’t find the thing you are looking for” (or I can but I am not going to tell you that)
We all know this one … but in an API context you need to check the “resource” which tends to be the numbers after the words
GET http://api.stuff.com/fruit/1234567
So, in this case, the fruit with the resource id 1234567 doesn’t exist
405 Method Not Allowed - "I know what you want to do and on what, but you can’t do it that way"
Check the method in your setup, are you doing a GET when it wants a POST ?
5xx - “It’s all gone horribly wrong at our end”.
Chances are it is them not you.