Change the line to an area
In Combo visuals, for better representation of data, CDP Data Visualization, enables you to convert the line to a semi-transparent area.
The default for combined charts is a bar measurement and a line measurement. To convert the line to a semi-transparent area (this enables you to see the bar chart, too), use the visual Settings interface, as described in Converting line to area.
To be able to clearly see the bars in a Combo chart, you can also specify a different axis for each of the measures in the bar and line chart.