Thank you Henric. I am making improvements.
After changing the chart type to grid chart, i checked advanced mode box and it allowed me to include 3 expressions:
1) this is my x axis where i want to see time (time stamp aggregated to day- level). but it is not understanding my expression (which is correct) that aggregates. its not letting simple transaction_date in the x-axis either. its counting transaction_date which is supposed to happen only in the 2nd expression
2) count(transaction_date): i intend to treat this expn. as Y-axis which is working well
3) sum(revenue): this is supposed to determine the bubble size, which is as expected.
one last issue: the bubbles are connected with a straight line as well. how to get rid of that.