Hi HB44, thanks for joining us here on the Community

We've got a handy guide here which covers how to customise the forms, though there are specific fields including the custom fields and email message which are interlinked with the main settings (Cog > Account & settings > Sales) and as such are not able to be customised per invoice. We appreciate it would be great to have these as seperate customisable fields per form and we'd be grateful if you could pop any feedback you have for this over to us by going to the Cog > Feedback - this way it'll be submitted directly to our developers for consideration. :)

Many thanks for your help Georgia and the information.  I have sent feedback as advised.