Lab 12.1. Create a Basic squid Forward Proxy

Hello,

i have some problems with this excercise.
The networking part is still a learning curve for me.

I´m now trying to configure the firefox browser to use the squid proxy.
But i can´t get it work. I get always this error "The proxy server is refusing connections"

squid -k parse
does not show errors.

the ip route command on my VM show this IP details:

default via 10.0.2.2 dev enp0s3 proto dhcp metric 100 
10.0.2.0/24 dev enp0s3 proto kernel scope link src 10.0.2.15 metric 100 
169.254.0.0/16 dev enp0s3 scope link metric 1000 

So I used this config for /etc/squid/squid.conf
acl examplenetwork src 10.0.2.0/24

and in this section: #http_access allow localnet

http_access allow localhost
http_access allow examplenetwork

In firefox i added this proxy setting under manual proxy configuration:
10.0.2.0 on port 3128

Where is my mistake here?