Full Idea
Kant denied that 'exists' was a predicate that enlarged the concept; he never denied that it was a predicate.
Gist of Idea
Kant never denied that 'exist' could be a predicate - only that it didn't enlarge concepts
Source
report of Immanuel Kant (Critique of Pure Reason [1781]) by M Fitting/R Mendelsohn - First-Order Modal Logic 8.4
Book Reference
Fitting,M/Mendelsohn,R: 'First-Order Modal Logic' [Synthese 1998], p.171