SendGrid is an email sending service that can make your email receipt delivery much more reliable.
Their WordPress plugin makes connecting Sliced Invoices to your SendGrid account simple. There is, however, a known issue with SendGrid causing problems with the invoice links that Sliced Invoices includes in emails you send to your clients.
If you are using SendGrid and are experiencing problems with invoice links not working, please follow these steps:
It should look like this:
File download links in email receipts should now work properly. If, however, they continue to fail, you will need to disable Click Tracking completely on both HTML and plain text emails.