There are times when a browser's cache data becomes full of frequently-accessed pages or damaged. This is the possible reason why you're clients can't view the detail of their invoice.
To help fix this, I recommend having your clients access their QBSE account via a private browser and view the invoice details from there. It's a great way in isolating the issue since it doesn’t store data in the cache.
However, if the issue persists, I recommend contacting our technical support team. This way, they'll be able to investigate what causes the issue and provide other troubleshooting steps: To contact us, please click this link: Contact QuickBooks Self-Employed Support.
To know more on how the Invoice feature works in QuickBooks Self-Employed, you can check these articles:
I'm here to share some information with you about customers unable to view invoices sent.
We have received several reports regarding this, and our Product Engineers are now working to fix it as quickly as possible. While they do, I recommend reaching out to our Customer Care Team, so you'll be added to the list affected users. To reach them, click the Assistant button at the top-right corner and type in Talk to human. Ensure to review their support hours so, you'll know when agents are available.
As a workaround for the meantime, you can export the invoice as PDF and manually send it your customers via email.
Here's how to export the invoice:
In the left menu, click Invoices.
Locate the invoice you want to send.
In the ACTION column, click the drop-down arrow beside the View link.
Thank you for your patience while we work for a fix. If you have additional assistance while managing your QuickBooks account, let me know. I'll be around to provide further assistance. Have a nice day.