Error: "Order not found"

A customer keeps trying to purchase things through my (Advanced Commerce) page, and when attempting to check out, continually gets the following:

{"error":"Order not found."} 

... see screenshot attached. 

She said it's the same whether she tries with credit card or PayPal. 
None of my other clients have reported issues. This client has purchased successfully in the past.

I couldn't find any other threads with this text. Any ideas?
Rachel

5 hours ago, inspiredrachel said:

A customer keeps trying to purchase things through my (Advanced Commerce) page, and when attempting to check out, continually gets the following:

{"error":"Order not found."} 

I’ve only seen this error when there’s a rare platform-wide issue, but there are no reports of this in the last 24 hours. If you are still experiencing this issue, please contact Squarespace Customer Support to report this directly.