Invalid indentation was detected!

A TMDL file mixes spaces and tabs, or uses spaces to indent; TMDL requires consistent tab indentation.

Why it happens

• Mixed spaces and tabs — e.g. a /// comment indented with spaces while the measure uses a tab.
• Spaces used inside a multi-line DAX expression.
• A standalone // section-header comment at measure level (only /// is valid there).

How to fix it

1. Use tabs only for indentation, never spaces.
2. Use /// for measure documentation, not //; remove standalone // section headers.
3. Run the model validator before opening in Power BI Desktop to catch it early.