Combining data from sheet in a dashboard chart

Hi everyone,

I have a form that I use internally to generate analytics. I am manually adding a certain "amount" per day. I want to visualize how much "amount" I have accumulated per month.

The form has a "date" and "value" property which get added to a sheet as "Date" and "Amount". I created a helper column to calculate which month it is:

In my chart I am using "Amount" and "Helper month" to visualize the amount. I want to visualize a combined amount in my chart, but currently it shows it as an individual:

Is there a possibility to combine the months?