This error is often caused by a small validation issue in the manifest, even if nothing obvious was changed. Double-check the manifest against the latest schema, especially required fields, app IDs, and formatting (commas, quotes, length limits). Re-exporting the manifest from the Teams Developer Portal and uploading it again also fixes it in many cases. If not, clearing cache or trying a different tenant/admin account can help isolate the issue.
Sometimes fixing Teams manifests feels more frustrating than Unfallwagen verkaufen.
