Payment Email Reminders

[codingsuks]

Has anyone found a shopify payment reminders app that can have custom flows depending on the manual payment someone selected? We have a few manual payments on our website and hoping to have an automation to remind customers of unpaid orders instead of having staff manually reach out. Only app I found that can do this is Kindly which takes a percentage of orders so is immediately a no go. Has anyone had success using the shopify api to start klaviyo flows?