What does default prove up mean?

The Plaintiff goes to Court with proof of service and the debts and gets a default Judgment.

what does default prove up mean?

It's a sort of one-sided mini trial wherein the Petitioner/Plaintiff puts on his case and evidence, a judges examines it, makes a decision and then enters a judgment (usually though not necessarily) in favor of that party. It's the way, and only way, a case can be brought to a conclusion when a Respondent/Defendant fails or refuses to take part in the case.