How can I merge two tables into one formula?

Hello dear Zoho community,

I would like to create a graph for my dashboard, where the Total Direct Costs / Client can be seen according to the respective month. However, this is currently causing problems as this data comes from two different tables.

Table 1: Number of Clients + Year & Month (X-Axis; User Filter)

Table 2: Total Direct Costs (aggregate formula from the different cost centers)

If I now use a simple formula, like:

"Commercial KPIs - Costs. "Total Direct Costs"/sum("Commercial KPIs - Clients. "Active Client")

and then create a chart and define Year & Month as X-axis, I don't get any data?

What is the reason and how can I solve this problem?

I hope you can help me with this, many thanks in advance!

Kind regards,

Luca