link - docs.microsoft.com/en-us/office/dev/add-ins/excel/custom-functions-troubleshooting
Add-in Error No Longer Available
This add-in is no longer available from the following server.
Check that the manifest file is correct and can be loaded.
Function Returns #BUSY!
Any registered custom functions will get saved and cached by Excel.
When a custom function cannot find its corresponding registration/add-in manifest file it will return #BUSY!
Check that the corresponding manifest file is correct, available and can be loaded.
Function Returns #N/A
Check the IDs are unique.
Check the IDs in the 'tsx' file correspond to the IDs in the 'json' file.
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