The first thing to check is which WooCommerce email notification you’re attaching the invoice to. You can verify this under WooCommerce > PDF Invoices > Documents, select the document type, then scroll to Attach to:
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Remember to check that you have the correct document type selected while in the Documents tab:
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Using MailPoet, Sendgrid, or another similar transactional mail service? #
Some of these services either don’t allow attachments, have capped the attachment count to 1 document or have capped the file size limit to 1 MB.
How to track your mail #
In addition to answering the above question, please follow these steps to find out if the issue occurs before the message is sent:
Install and activate the WP Mail Logging plugin.
Go to Dashboard > WP Mail Logging > Settings, and enable the Display Attachments option:
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Open an existing order, find the Send order email panel, on the right side, select one of the email notification in which you attach the invoice.
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As an example, you could select Completed order, then click on Save order and send email.
Then go to Tools > WP Mail Log, find your last email & check if there are files in the Attachments column and/or any notice on the Error column.
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Lastly, share the results with us. 🙂