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
If you're still having issues, hit us up, we'd be more than happy to investigate.