You might want to double-check that the option to attach a PDF file is selected. Here are the steps to complete the process.
Click on the Gear icon at the upper right corner and choose AccountsandSettings.
From the Sales tab, tick the Online delivery to edit.
Select on the Showfulldetailsinemail radio button. Make sure to put a check-mark on the PDFAttached box.
Tap on Save.
However, if this option is selected, let's access the email that you've sent on a private window. At times, the stored data on the regular browser may lead to unusual behavior like the missing PDF attachment of the invoice.
If you're able to see the PDF attachment on the invoice, you may clear the browsers' cache to remove the unnecessary data and refresh your files. It also prevents this hurdle from occurring.
For more details about the different file types that you can attach to any transactions in QBO, together with thing that you need to know when emailing them, please see these links below:
I send my invoices as a pdf attachment and since Friday it is not being sent as a pdf. How do I correct this feature?
Thanks for your replies. I do already have my settings set for PDF to be attached. I think the problem was that I started using the "duplicate" function to create my invoices (i.e., I duplicated a previous invoice to the same client, revised and saved as new invoice). Apparently, when you do that, the PDF of the invoice won't be attached to the email. So I went back to creating new invoices for every invoice.