If you wish to write a personal message within the email that is sent to your client which contains your invoice attachment, then this is possible though not always obvious at first! So here’s how:
By using the Line Items feature in order to itemise/list things within your invoice (accessed via the ‘+ add items’ button which appears in the total amount field when you tap it); this will activate anything you write in the ‘description’ field (the field below the total amount field) to become an attached note/message in the email sent to your client. Please note, it will be entirely separate to the actual invoice itself. Therefore, this space is often used to say ‘hello’ or ‘thank you’ to clients, unless it is needed to include other information which does not fit or is not required on the actual invoice template itself. Please note that the ‘description’ field will ONLY be activated in this way, when or if the Line Items feature is used - and not otherwise.