I sent a test invoice to myself. I clicked the link in the email and it went to a page where I got this message:
This webpage is not available.
The webpage at https://fanceymarketing.com/invoice/?invoice_id=897b61df8ef8e8d51046aa2be398066c might be temporarily down or it may have moved permanently to a new web address.
More information on this error
The main site loads fine, just the invoice URL that doesn't seem to work.