That may be by design. If you're requesting a resource and it doesn't exist, Doshii will send you back a 404 for your trouble.
For example, on the endpoint https://sandbox.doshii.co/partner/v3/orders/8349823; Order ID 8349823 doesn't exist (yet) hence a 404!
If that doesn't help, double check the URL for typos, can be easy to mix up ordersand order.
If you're still having issues, hit us up, we'd be more than happy to investigate.