Can't get access digi wr21 when i downgrade

Hi everyone I’m having logging problem when i downgrade firmware with 6.x.x

When i downgrade and restarting digi it doesnt accept username and password

Username : username
Pass : passsord

Or

Username : admin/Admin
Password : password

Or

Username : admin/Admin
Password : on the bottom of the digi

None of them accepting.

Default user credentials depend on how the downgrade was done, with Web UI or with Flashwriter.
You can try the leftover option: admin/default
Please see details below:

DEFAULT USER ACCOUNTS
Previous firmware releases for the WR11, WR21, WR31, and WR44 devices included a default user
account with the credentials username/password. With firmware release 8.0.0.3, new routers will
no longer include the default username/password account. Instead, routers manufactured with
firmware release 8.0.0.3 will now have a default admin account and a pre-programmed unique
password that is displayed on the device label.
Special consideration must be given when upgrading or downgrading devices that cross this
functional boundary. The following special cases apply:

  1. Upgrading routers that were manufactured prior to 8.0.0.3 (for example, 7.1.2.2):
    a. If you upgrade the firmware to 8.0.0.3 using the Web UI Update Firmware1
    , the router
    retains the existing default user accounts. For example, after the upgrade, the router
    will have a default username/password account running 8.0.0.3.
    b. If you upgrade the firmware to 8.0.0.3 using Flashwriter, the default account will be
    admin and the password will be default.
  2. Downgrading routers originally manufactured with 8.0.0.3, that include an admin account with
    a pre-programmed unique password:
    a. If your router is running 8.0.0.3 and has the admin account with a pre-programmed
    unique password, and you use the Web UI Update Firmware to downgrade to a release
    prior to 8.0.0.3, the downgraded router will no longer recognize the pre-programmed
    unique admin account password. Instead, the admin account password will be default.
    b. If your router is running 8.0.0.3 and has the admin account with a pre-programmed
    unique password, and you use Flashwriter to downgrade to a release prior to 8.0.0.3,
    the admin account will no longer be present. Instead, the default account will be
    username/password.
    i. After downgrading with Flashwriter, if you then upgrade to 8.0.0.3 or greater
    using the Web UI Update Firmware, the router will retain the
    username/password account and not include an admin account.
  3. If you then factory default the router, the admin account with the preprogrammed unique password will return.
    ii. After downgrading with Flashwriter and losing the admin account, if you then
    upgrade to 8.0.0.3 or greater using Flashwriter, the admin account with the preprogrammed unique password will again be present and the
    username/password account will be removed.