Are you trying to create a new company in Microsoft Dynamics 365 Business Central and running into the error: Sorry, your Dynamics 365 Business Central account is locked for new companies. Your company has used Microsoft Invoicing, which is where you got your Dynamics 365 Business Central account, and that account allows only the two companies it came with. Contact a Microsoft partner or Microsoft support and ask them to unlock it for you? Here's what to do to fix this...
Disclaimer: You should always contact your Microsoft Partner before making any changes to your Business Central tenant. We do not recommend you do the following without the help of your Microsoft Partner or Solution Systems.
This issue is related to the Microsoft Invoice which is found in Office 365. Microsoft Invoice and Microsoft Dynamics 365 Business Central do not mesh well together. So, to solve this issue here are the steps needed:
Access the Admin Center
Once in the Admin Center select the environment in which you encounter the error message (on the screenshot example below it will be the first one).
Click on "Delete" (When deleting wait anywhere from 7-10 minutes, then click on "Refresh")
Once you see the environment has been deleted, click on "New", and select the values requested by the system.
Wait until you see creation is completed (usually takes about 10 minutes, if it doesn't show as completed wait a few minutes more and click Refresh).
Once you see it completed, you access the environment and should be able to continue.