My recorded request do not have "If-Modified-Since" field in the header. However during playback Neoload automatically adds this field with some timestamp. This results in server responding with http status code 304 instead of expected 200. Can I know why is Neoload inserting this field, and how does it determine the timestamp value.
This header is related to the cache of the resources. It is added to check if the resource has been modified on the server side.
When it is not the server replies back with a 304 which is completely normal. That means no need for the client to download the resource again since it has not been modified since the last check.