Solution 1:
`# Remove .php extension
RewriteRule /.*/?$ - [L]
RewriteCond %{THE_REQUEST} ^GET\ /[^?\s]+\.php
RewriteRule (.*)\.php$ /$1/ [L,R=301]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^/(.+)/$
RewriteCond %{DOCUMENT_ROOT}/%1.php -f
RewriteRule ^(.*)/$ $1.php [L]

# Force trailing slash
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule .*[^/]$ $0/ [L,R=301]`

Solution 2:
`# Remove .php extension
RewriteCond %{THE_REQUEST} ^GET\ /[^?\s]+\.php
RewriteRule ([^/]*)\.php$ /$1/ [L,R=301]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} ^/(.+)/$
RewriteCond %{DOCUMENT_ROOT}/%1.php -f
RewriteRule ^([^/]*)/$ $1.php [L]

# Force trailing slash
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule [^/]*[^/]$ $0/ [L,R=301]`