Thank you JimmyKater
I will try to translate :
The problem is with BBB , i installed it and create a room but when i run it a new tab is opennig with error , so i browse the events and i have this message 
Exception: String could not be parsed as XML
/var/www/html/nextcloud/apps/bbb/vendor/bigbluebutton/bigbluebutton-api-php/src/BigBlueButton.php - line 494:
SimpleXMLElement->__construct("<!DOCTYPE h … n")
/var/www/html/nextcloud/apps/bbb/vendor/bigbluebutton/bigbluebutton-api-php/src/BigBlueButton.php - line 112:
BigBlueButton\BigBlueButton->processXmlResponse(“api/create? … 6”, “”)
/var/www/html/nextcloud/apps/bbb/lib/Controller/JoinController.php - line 143:
BigBlueButton\BigBlueButton->createMeeting(BigBlueButto … {})
/var/www/html/nextcloud/apps/bbb/lib/Controller/JoinController.php - line 110:
OCA\BigBlueButton\Controller\JoinController->processPublicJoin(OCA\BigBlueB … 5}, “AdminCloud”, “welcloud”, null, null)
/var/www/html/nextcloud/lib/private/AppFramework/Http/Dispatcher.php - line 170:
OCA\BigBlueButton\Controller\JoinController->index(“AdminCloud”, null, null)
/var/www/html/nextcloud/lib/private/AppFramework/Http/Dispatcher.php - line 99:
OC\AppFramework\Http\Dispatcher->executeController(OCA\BigBlueB … {}, “index”)
/var/www/html/nextcloud/lib/private/AppFramework/App.php - line 125:
OC\AppFramework\Http\Dispatcher->dispatch(OCA\BigBlueB … {}, “index”)
/var/www/html/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php - line 47:
OC\AppFramework\App::main(“OCA\BigBlu … r”, “index”, OC\AppFramew … {}, { token: "x8 … "})
<>
OC\AppFramework\Routing\RouteActionHandler->__invoke({ token: "x8 … "})
/var/www/html/nextcloud/lib/private/Route/Router.php - line 299:
call_user_func(OC\AppFramew … {}, { token: "x8 … "})
/var/www/html/nextcloud/lib/base.php - line 1008:
OC\Route\Router->match("/apps/bbb/b/x8FNRmBCjxBeTMZL")
/var/www/html/nextcloud/index.php - line 38:
OC::handleRequest()
Did you have any idea of what’i wrong with my installation ?