Reverse proxy with slash

Hello everyone ,
I’m sorry to post my question here but I did a lot of research on the internet and I can’t find the solution.
I am an intern in a company and I am a beginner in computer science and even more in English.

i want to use haproxy as proxy reverve (i will try to explain in my words forgive me.)

We have a single public ip address (example that we want to use to call several servers locally (from the outside) using the reverse proxy
(example the glpi server accessible only in
and another one based on server

the fixed ip address of the haproxy is (example)
the forti redirects the public ip to the haproxy
the port used is 80

but I can’t do it with the configuration
I block for example on the backend part

we can only redirect to an ip
backend my_backend
glpi server
while I want
backend my_backend
glpi server

when I type from the outside, I find the page of and not the page of

I don’t know if I explained correctly, again sorry for my English and thank you again for the answer you will bring

version haproxy 1.8 on debian 10