important status code to be known as API developer

success
200 ok

• use with get method after receiving success response

201 created

• use with post method when data is add or modify in database

client error
400 bad request

• use when user send wrong data with payload, parameter or query

401 unauthorize

• use when unauthorize user or without login user try to access the resources.

403 forbidden

• use when user is authorize but not have permission to access the resources(admin).

404 page not found

• use when user try to access invalid route.

server error
500 internal server error

• when something went wrong with code or server.

*for more refer *