Customer can't view invoice

When I email an invoice the customer can read the body of the email but cannot view the actual invoice.
I’ve resent to several customers and they all say the same.
One told me they tried with Safari and Google, both won’t open. I’ve attached a screen shot of what she sees when clicking on “view”.
I sent myself an invoice and I could view it but none of my customers can.
I’m using a desktop computer and version 23.12.12.1221 of manager.
This has only happened since I updated to this version.
Any advice would be appreciated.
Screenshot 2024-01-05 092220

Thank you @Mabaega. I went to settings, obsolete features and enabled PFD and now it works.