Dynamics 365 Business Central External Accountant can only be purchased as an Addon to an existing Business Central Essentials.

Designed for businesses that have outgrown their basic accounting software.
Microsoft Dynamics 365 Business Central is a business management solution that helps companies connect their financials, sales, service, and operations to streamline business processes, improve customer interactions and make better decisions.

IOTAP Business Basic provides online access to your favorite productivity apps; Microsoft Word, Powerpoint, Excel and Outlook as well as Microsoft-hosted email using Exchange. In addition to meeting your productivity needs, Business Basic also screens incoming email links and attachments for any malicious intent.