App Service Migration: Error: RegisterTool error

Whilst using the Azure App Service Migration Assistant tool to migrate an IIS app to Azure App Service, on the Azure Migrate Hub screen, after selecting a project and clicking Send Migration Data, we got the below error:

• Step:

  Sending server discovery data to Azure Migrate (step 1 of 1).

• Error message:

  Step error details: Error: RegisterTool error: Error: RegisterTool error: Error: Error registering Tool: [object Object]

It's unclear from this what the error is / what steps we should take to better understand the cause / resolve the underlying issue.  Any advice on how best to proceed would be appreciated.