Error 21503 using REST connector for a copy activity -

Hi pmscorca,

Since Organizational account is not available in the dropdown for Web connection, Need to switch from using a Web connection to a REST connector configured with supported authentication types. 
By follwoing bellow steps yo can try to achive this.

Option 1: Use Service Principal

This is the most reliable workaround. Go to Azure Portal and register an app.

Generate - Client ID - Client Secret - Tenant ID

Assign necessary API permissions to the app for Business Central.
In Fabric, create a new REST connection using.

Authentication type: Service Principal - Provide the above credentials and use this connection in your copy activity.

This avoids the OAuth2 limitation and works seamlessly with Business Central’s API.

Option 2: Use Organizational Account via Dataflow Gen2

If it insists on using Organizational account, You needs to use Dataflow Gen2 instead of a copy activity and in Dataflow Gen2, the Organizational account option is available and supported for Business Central by Authenticate using Azure AD credentials and pull the data.

If still wants to use Power BI Desktop to test the connection.

• Connect to Business Central via OData connector.
• Copy the M code from Power Query.
• Paste it into a blank query in Dataflow Gen2 in Fabric
  
  

Thanks,
Akhil.