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HA proxy to drop connection which includes string

I am using HA proxy as a loadbalancer. I need to drop all requests which contain the string in the middle of request. I found out the solution like silent-drop
my additions in settings look like that:

acl restricted_page path_sub,url_dec -i my_string
http-request silent-drop if restricted_page

But when I doing the request it still showing an output, even when I used "deny instead of silent-drop it doesn’t work as I wanted. Anyone know the right soultion of that?