https://developers.pipedrive.com/docs/api/v1/Activities#getActivitiesCollection
I could not understand the response of this endpoint.It returns the records which are not in UI(it may be deleted),how to differentiate these records.when I pass the id of some records to Pipedrive API v1 Reference ,it shows activity not found.Kindly sort it out this doubt.
Hello @Tanikha_S 
The GET /activities/collection endpoint currently returns also soft-deleted activities, meaning activities that were deleted up to 30 days ago. The fact that you consider this a confusing behavior is very good feedback for us and I have forwarded this to our team! 
As the endpoint is in Beta, we are taking into consideration all feedback we receive to possibly make changes to the endpoint’s behavior.
I have reached out to you via private message to learn more about your experience using this endpoint!
Sincerely,
Helena