Hi @cmpengineers
From buy now api you mean when customer click on buy now so product added into cart and customer directly redirect to checkout or view cart page, please correct me if i am wrong.
So for this you have to do customisation in add to cart api.
First of all you need to pass
is_buy_now in parameter with value
true.
Now go to add to cart api controller here if condition is already there related to is_buy_now.
Now you need to add some custom parameter in return response so that you could identify that customer is using buy now btn instead of add to cart.
So at the last whenever you received your custom parameter in response so redirect the customer to the desired page.
You can implement this in both ways by adding new controller or modify existing add to cart controller.
Thanks