1
general::
Make a mistake, blunder, as in I slipped up and gave the invitations to the wrong people. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): slip up something
to climb something, slipping along the way. • The hikers slipped up the wet slope. • Ted slipped up the stairs, tracking mud and water as he went along.
McGrawhill's American Idioms And Phrasal Verbs