SQL Server Mirroring keeps giving error when I want to add more tables

[sholy29]

I currently mirror SQL Server from our on-prem SQL Server to Fabric. I have couples of table currently mirrored to fabric. I want to add more tables to mirrored, but when i click on the configure replication to add more table, I keep geeting the following error

The error: The database cannot be mirrored to Fabric due to below error: Test connection failed. Request failed with status code 400 Activity ID: undefined

Mirroring still works fine for other tables that were previouslly added. I am really confused about. On a few occasion it just work but most of the time, i get the above error.

I will appreciate any help or pointers. Thanks

[v-karpurapud]

Hi @sholy29 

I wanted to check if you had the opportunity to review the information provided. Please feel free to contact us if you have any further questions. If my response has addressed your query, please accept it as a solution and give a 'Kudos' so other members can easily find it.

Thank you.

[v-karpurapud]

Hi @sholy29 

Welcome to the Microsoft Fabric Community Forum. 

The error encountered when attempting to add more tables to an existing SQL Server mirroring setup in Microsoft Fabric, specifically “Test connection failed. Request failed with status code 400,” is typically caused by transient backend service issues, gateway misconfigurations, unsupported schema elements, or disabled tenant settings. While previously mirrored tables continue to function, new additions may trigger revalidation processes that expose these underlying issues. 

To resolve this, retry the operation after a short delay, as transient errors often self-resolve. Additionally, ensure the on-premises data gateway is properly configured and restarted, and that SQL authentication is used for connectivity. Review the schema of the new tables to confirm they do not contain deprecated data types such as TEXT, NTEXT, or IMAGE. 

In the Microsoft Fabric Admin Portal, verify that the tenant setting “Users can access data stored in OneLake with apps external to Fabric” is enabled. If previous mirroring attempts left residual metadata, use SQL commands such as sp_change_feed_drop_table_group to clean up stale entries. Finally, add tables incrementally and monitor replication status using diagnostic views like sys.dm_change_feed_errors to isolate and address specific issues. These steps have been validated across multiple incident reports and align with Microsoft’s recommended practices for ensuring reliable mirroring to Fabric.

If this response resolves your query, kindly mark it as Accepted Solution to help other community members. A Kudos is also appreciated if you found the response helpful.

Thank you for being part of Fabric Community Forum.

Regards,
Karpurapu D,
Microsoft Fabric Community Support Team.