How are you handling the AR process after Salesforce CPQ generates the invoice?

Once invoices are generated, how are you managing payment reminders, dunning, and collections follow-up? Custom Flow/Apex, a third-party AR tool, or still manual chasing in Service Cloud or spreadsheets?  

Disclosure: I work on Quick Receivable, an AR automation app for Salesforce. Genuinely curious what teams here are doing post-invoice, not trying to pitch anything.