One client's authority was split across trailing-slash twins

One client's authority was split across trailing-slash twins
Same page reachable at /category AND /category/. Both 200-status. Both indexed. Links split between them. Two weak pages instead of one strong one.
The move:
— Picked one form (slash for folders, no-slash for files — pick a rule and never break it).
— 301 the loser to the winner at the server level. Not a meta canonical — a real redirect.
— Fixed internal links so they all point at the canonical form. Stop relying on the redirect to clean up your own sloppy <a> tags.
— Same fix for www vs non-www and http vs https. Four versions of every URL is the default WordPress disaster.
Watch uppercase. /Category and /category are different URLs on most servers. Force lowercase in the redirect rules too.