Hello @SatishB721,
Thank you for reaching out to Constant Contact's API Support.
I tested this and despite our example text it does require that you have a timestamp listed as well. I tried with start=2015-09-01T00:00:00-0500&end=2020-04-05T00:00:00-0500 and it worked just fine. I'll double check with our backend and see why the time is required despite our documentation.
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