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Hello there,
This error is usually caused by a mistake when you write code or copy and paste the code in advance query. You can do these to check the error: click "Show error" and then it will show you where is no comma in the code.
This article provides suggestions for how to fix the most common errors you might find at each level and describes the error reason, error message, and error detail for each. https://learn.microsoft.com/en-us/power-query/dealing-with-errors
The below thread discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
https://community.powerbi.com/t5/Report-Server/Error-Token-Comma-expected/m-p/1636405
Hope this resolves your Query !!
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