How to handle the division of metrics by empty or null values?

Could you please check if the metric Discounts and Gross_Sales share the same dimensions?

Hello, yes, it shares the same dimensions. Thank you for your help.

What does this warning say? Or you may want to lay out the metrics at the very bottom level and make sure there are values from both metrics at the same intersection instead of the aggregation level.
 

I aligned all the Metrics with their s dimension so that Discount and Gross Sales have the same structure; I no longer get an error message, but this does not solve the problem.

Now you have 7 dimensions in your final metric. In your metric of Discount_EUR, I noticed that the customer dimension is not included from your previous screenshot.