How are you all handling milestone billing for client projects?

One thing I didn’t expect when running a small service business was how messy milestone billing can get. On paper it sounds simple — break a project into phases, invoice per phase — but in reality the details end up scattered everywhere. Scope in one place, deliverables somewhere else, notes in email or Slack, invoices generated separately. It works… until a client asks what exactly was included in a specific milestone and you’re digging through old threads trying to piece it back together.

I’ve been trying to clean up my process so milestones, deliverables, and invoices are more tightly connected, mostly to avoid billing mistakes or awkward back-and-forth. For those of you running service-based businesses, how are you handling milestone tracking and invoicing? Are you using spreadsheets, accounting software, PM tools, or some hybrid setup?