If the default credentials do not work and you've forgotten your custom password, use these recovery methods from Recovery Squad : NVR/Basic Setup/Initial Setup - DahuaWiki
If you are trying to access a Dahua DVR and admin/admin does not work, the device is either modern or has been secured. Do not attempt brute force – use the physical reset or Dahua's password recovery tools. dahua dvr default password
While admin is typically case-insensitive on the local machine, web logins are often case-sensitive. Ensure "Caps Lock" is off. If the default credentials do not work and
Dahua's authentication schema has shifted over three distinct eras. Below is the matrix of known default states based on firmware versions and product lines. Ensure "Caps Lock" is off
Most Dahua devices manufactured recently no longer have a universal default password. During initial setup, the system forces users to create a unique, strong password. If you are prompted for a password on a brand-new device, it is likely the one set during its first-run initialization. How to Reset if Locked Out