[Plugin: PHPBB Single Sign On] Problem with Php Single Sign On

Hello, I just installed the plugin and I would like some information please.
Logically, everything is set up because everything is OK write on each line. However I wonder if a, I must enelever entries from wordpress? Is what I have to leave to allow users to register on both (WordPress and PhpBB)? For now, I leave that:

1-Wordpress: allow users to register …. Members become “Subscriber”
2 – PhpBB: Authentication: wpbb

If ever someone tries to connect or to register, here’s what happens through WORDPRESS:
SQL ERROR [mysql4]

Duplicate entry ‘zedole’ for key ‘username_clean [1062]

An sql error occurred while fetching this page. Please contact administrator if this problem year Persists.

But if the person connects via the Forum and it launches the wordpress site, it will connect. Why is it that both ways it does not work? Ultimately, I can make a widget on the side for registration / login.
Even more suspicious, when I login with my administrator account, all goes perfectly …. Thank you to enlighten me on that and advise me on a possible change to be made.
Second concern, apparently, when I write on the blog, posts are not transferred on the forum.
Thank you and congratulations for the work ??

https://www.ads-software.com/extend/plugins/phpbb-single-sign-on/