Transparent proxy in bridge mode

[Mars79]

I've setup OPNsense in bridge mode as described in https://docs.opnsense.org/manual/how-tos/transparent_bridge.html
Afterwards I configured a transparent proxy server with web filtering also described within the docs and howto's.
I did bind the proxy server to the bridged interface, then added the firewall rule (from the option below the transparent proxy server setting). But no http traffic is coming through. I played with the firewall rule, changed the default rule from the LAN interface to the bridged interface, but so far no luck.
What rule should I use, or is it even possible to use a transparent proxy server while OPNsense is running in bridged mode?