FIXED – MS Flow HTTP 400 – Managed Metadata
Wanted to share resolution for tagging Managed Metadata term in MS Flow and seeing error HTTP 400. Managed Metadata terms are stored in SharePoint with GUID identifiers. That enables us to rename terms while preserving all current tag usage. However, it means that we must use GUID when adding and updating tag values to ensure lookup saves successful. Cheers 
Error
HTTP 400. The data returned from the tagging UI was not formatted correctly.
Resolution
Format text for Managed Metadata tag as “VALUE | GUID”. For example, here we have “JavaScript|6f634666-d2a6-4367-9b65-4bb4ab33afc6” in the MS Flow Set Variable set. Publish, run flow, and confirm SPListItem successfully added to demo list.
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