content-lengththat telsl the recipient how much body it should expect before finalizing processing the entire message and preparing the response. When working with web APIs you almost never set this header manually. However, the other very common header
content-typealmost always has to be set by you. This header tells the recipient what is the format of the incoming data. It can be JSON, XML, binary data of any form, and many more. You can also define your own set of headers that are only used by your particular API if that's really needed. However, the standard set of the headers usually is enough for the majority of cases.