In order for two devices in an High Availability configuration to share licenses for support, VPN, etc, they must first be associated in the mysonicwall.com account.
This article is designed to assist with this process.
Step 1: Go to  www.MySonicWall.com and log in to an account that the devices are registered to.
Step 2: Go to My Workspace and Tenant Products then Click on the serial number to which the secondary (HA) device needs to be associated

Step 3: Under Product Details click HA Secondary and select the Secondary device Serial Number from the provided drop down.
NOTE: If the intended secondary does not show up in this menu, return to the Tenant Products list and confirm that the device is visible here.

After the association is made, the message is shown as a banner: "Success: The association is added successfully"
TIP: If you wish to remove the association there is a trash icon under "HA Secondary".