To set up auto deductions to the invoice, create a recurring invoice first. Then when your client goes to pay it, instruct them to check the auto pay future invoices tab when paying the first payment and they will never have to worry about it again!
This feature is only available when connected with Stripe.
That simple! ;)
NOTE: You cannot create these recurring payment features in proposal yet. This can currently be done in jobs or leads. Once we know we have worked out any potential bugs, then we will allow your clients to be able to choose recurring from a proposal.