Microsoft have not only removed the 300 license minimum, but they have also removed the enterprise level license (E3/E5) restriction also, now Microsoft 365 Business Standard and Microsoft 365 Business Premium also able yto purchase the license!
For more details, please visit https://www.microsoft.com/en-au/microsoft-365/business/copilot-for-microsoft-365?icid=copilotblog&rtc=1#FAQ
