This article details how to Enable the SonicOS API on the SonicWall UTM devices
This release includes significant user interface changes and many new features that are different from the SonicOS 6.5 and earlier firmware. The below resolution is for customers using SonicOS 7.X firmware.
For Gen 7 firewalls, like TZ 270 or TZ4700, if you imported settings from a Gen6 firewall like TZ500, SonicOS API needs to be enabled for NSM management.
Here is how to enable SonicOS API in Gen 7 firewall:
Log into firewall, go to Device/Settings/Administration/(Audit/SonicOS API), enable it (see screenshot below):

NOTE: Enabling/disabling SonicOS API will not require reboot. But after enabling it, when NSM configures the firewall for AppFlow data, firewall might reboot depending on existing configuration.
This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.
Here is how to enable SonicOS API in Gen 6 firewall:
Log into firewall, go to Manage/System Setup/Appliance/Base Settings/SonicOS API, enable it.
NOTE: Enabling/disabling SonicOS API will not require reboot. But after enabling it, when NSM configures the firewall for AppFlow data, firewall might reboot depending on existing configuration.