How to Determine:
If the customer has included their access token in the "System Information" then you can determine if this is the cause by using your own test site to enter their token and see if a generic feed displays properly. If it's not included, you can view the page source and find it in the footer (see attached).
Generic Response:
It looks like your access token has expired. Occasionally this happens without warning or reason anywhere from a few weeks to years. It's something that Instagram does on their end so, unfortunately, we have no control over it. You can get a new access token by using the big blue button on the "Configure" tab or by using this link.
If you continue to have problems you can use the method described in this link as well.
Let me know if you need any more help with this!
