I came across with a problem to use Netbox REST API. And here is how I overcome that;
So in order to use Netbox API you need to add Authentication to your requests.
In your request go to ` Authorization ` tab and select API Key from the TYPE menu
in the boxes you need put : Authorization for Key
Token {Netbox API token } for Value
and Add to Header
This is actually one of the most common mistakes beginners face while working with NetBox APIs — thanks for pointing it out 
For anyone still getting 401 Unauthorized errors, here’s the exact way to fix it in Postman:
Open your request in Postman
Go to the Authorization tab
Select Type → API Key
Fill the fields as:
| Field | Value |
|---|---|
| Key | Authorization |
| Value | Token <YOUR_NETBOX_API_TOKEN> |
| Add to | Header |
After this, your request headers will automatically include:
Authorization: Token YOUR_NETBOX_API_TOKEN
Now your GET/POST/PUT requests should work without authentication errors 
Super helpful tip — this will save a lot of debugging time for newcomers!