If you followed the steps for importing events older than five days but your import isn’t working, here are the most common issues to look for first:
You’re using your project’s API Key instead of the API Secret or Token. To find your API Secret, click your user icon in the upper right hand corner of your Mixpanel project, select Account from the dropdown, and click Projects. This is easily confused with your API Key, but the distinction is important, as your import will not work if you use the API Key.
You’re importing events that have not been triggered in the past 30 days. Following import, events will not be displayed in Engagement reports if they have not been triggered for the past 30 days (i.e., they will be automatically hidden from the UI). If you aren't importing any recent events, try firing a "dummy" one with the same name to resurface old events and force the event to appear in the dropdown.
You’re not using valid JSON. You can try using a third-party JSON validator (like this one) to help debug.
If none of these is the problem and you’re still having trouble importing events for your current users, please reach out to firstname.lastname@example.org. Please include a sample HTTP request you are making.