Hi, Always read the release notes before flashing firmware.
DH_NVR5XXX-EI_MultiLang_-V4.000.0000000.1.R.230427.zip_Release-Notes
1.5.1 Program
After the earlier baseline V4.000.0000000.0.R.230131 is updated to this new baseline version or
later, it cannot be degraded to the original version.