Usually SEOs (me including) use 301 redirect for that purpose, which I had in my .htaccess but it stopped working once I switched to CloudFlare for some reason (or maybe because of something else I’m not aware).
The .htaccess rule I had is:
RewriteEngine on
RewriteCond %{REQUEST_URI} /+[^\.]+$
RewriteRule ^(.+[^/])$ %{REQUEST_URI}/ [R=301,L]