As of April 4th, 2018, if you want to show posts from someone else’s Instagram account, you will need his or her Access Token. You can retrieve this using the big blue button on the “Configure” tab while logged in on Instagram.com to the account you would like an access token from.
Alternatively, someone can send you their Access Token and you can then connect their account in the plugin manually. To do this, click the Manually Connect an Account button on the plugin settings page and enter it here. You will also need the User ID for their account.