Integrate an LDAP account database with Taiga

Not sure. If you can access the Taiga instance in the browser, and also see that you can send and receive to and from the API (which you proved by posting the network inspector screenshots), then the script provided in my other answer should not give you any further information.

The next thing I would try is jumping into the backend container again and see if you can temporarily install ldapsearch there and execute a query against the LDAP server.

If it works, this means the problem must indeed be the LDAP plugin. If it does not work, likely something else is afoul with the communication.

Test LDAP connection using base ldap-utils

  1. Enter the container:

    docker exec -it taiga-taiga-back-1 bash
    
  2. Install ldap-utils:

    apt update
    apt install -y ldap-utils
    
  3. Start LDAP search:

    ldapsearch -H ldap://sso.yourdomain.example -D "cn=admin,DC=yourdomain,DC=example" -W -b "OU=people,DC=yourdomain,DC=example"
    
  4. Enter bind password:

    Enter LDAP Password:
    
  5. Check exit status

    echo $?
    

The exit status should be 0 (success). If not, this means that not even Linux standard utilities can access the LDAP server from the backend container.