The Hinari Mobile app (for Android/iOS) sometimes bypasses UPD browser issues. Download the app, select your institution, and use the mobile-specific login flow.
If you are a new user or have forgotten your credentials, you cannot randomly guess them. The UPD has a specific recovery flow. hinari+login+username+password+upd
Once you've registered and your application has been approved (which might take a few days), you can log in to the HINARI website. Go to the HINARI homepage, click on the "Login" button usually found at the top right corner, and enter your email address (which serves as your username) and your password. The Hinari Mobile app (for Android/iOS) sometimes bypasses
If your institution is registered, the official username and password are held by the university librarian or the director of the institution. The UPD has a specific recovery flow