Hey @clickvesa, and welcome to our community 
In your case, and from the perspective of just creating a branch, this is the expected behavior.
The fact that you want a complete list of branches associated to a company is a specific behavior, so a bit of code will be required.
If you want to update the company when creating a branch (In order to have the complete list of branches associated to the company), you’ll need to override the POST /branches route in order to update the company as well.
Let me know if that helps 