I have been going round is circles trying to achieve the following and wondered if it's even possible, my data is sourced from a SQL database.

I have a stacked bar chart that shows 'sum of sales by date and category'. Additionally I have attempted to plot a target figure on the secondary axis, this gives me a line per category. What I actually need is the sum of the target, i.e. just one line plotting the aggregated target per date.

Is this even possible?