A quick fix when encountering the 403 forbidden error while updating minify settings with W3 Total Cache is to disable Apache’s ModSecurity, as it conflicts with W3TC when updating the minify settings.
ModSecurity/Apache will throw an error like the one below:
ModSecurity: Warning. Match of “rx ://%{SERVER_NAME}/” against “ARGS:minify__cache__files” required. [file “/etc/apache2/modsecurity.d/rules/tortix/modsec/50_plesk_basic_asl_rules.conf”] [line “386”] [id “340465”] [rev “56”] [msg “Protected by Atomicorp.com Basic Non-Realtime WAF Rules: Remote File Injection attempt in ARGS (admin.php)”] [severity “CRITICAL”] [hostname “youdomain.com”] [uri “/wp-admin/admin.php”] [unique_id “WbLrG38AAAECADaiJGUACCAB”]
Thanks for the hint BTW!