This only applies to Xero
Xero doesn't send the attachment with the email when the email is triggered by an external system like SortScape. When using Xero with Sortscape, invoices are created and managed entirely within the Xero system. Sortscape is responsible for sending the invoice details to Xero, which then takes over the invoicing process. This ensures that users can leverage Xero’s robust invoicing capabilities while Sortscape facilitates the integration by transmitting key details.
Xero are aware of the limitation and have an open feature request where you can vote on fixing this here https://xero.uservoice.com/forums/5528-accounting-api/suggestions/39240961
To address the PDF attachment limitation, users can send invoices through Sortscape instead of Xero. By using this method, the invoices will include the PDF attachment, effectively addressing the API restriction.
Please contact support to have this enabled for you.