Harvest does have retainers and recurring invoices: <a href="https:&#x2F;&#x2F;www.getharvest.com&#x2F;help&#x2F;invoices-and-estimates&#x2F;invoices-estimates-faqs&#x2F;recurring-or-retainer" rel="nofollow">https:&#x2F;&#x2F;www.getharvest.com&#x2F;help&#x2F;invoices-and-estimates&#x2F;invoi...</a><p>(Disclosure: I work at Harvest)