Create the following registry value on the Veeam Backup Server, replacing <SubscriptionIDs> with a list of Azure Subscriptions IDs that should be used by Veeam Backup & Replication when adding an Azure Compute account.
Key Location: HKLM\SOFTWARE\Veeam\Veeam Backup and Replication\
Value Name: AzureSubscriptionIdsToInclude
Value Type: Multi-String Value (REG_MULTI_SZ)
Value Data: <SubscriptionIDs>
Each Subscription ID should be on its own line.