Invoicing - Follow up email after payment
It would be useful to be able to send an email to a customer xx days after an invoice is paid.
This could be used for all sorts of things from offering discounts on new orders to reminding them to leave a review for your service. A bit more of a CRM style feature but would help with business workflow and keeping actions in one place.

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Georgia Johnston commented
In the contact details area, when creating a new invoice, would it be possible to create a checkbox that can be ticked to send automated reminders to a customers email/phone number, reminding them to book in for their 12 month service. In this instance, pest control services.
The screenshot of the invoice below, is a task of a job that's completed annually.