Can't log in into admin area

[Executable]

I'm trying to login into my admin area using my correct credentials. then I click on login button, I'm redirected into this page : 

 

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Something went wrong and we couldn't process your request.

Please go back to the previous page and try again.

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Here is what I got from my webserver log : 

 

2019/09/23 15:34:40 [error] 29188#0: *13488328 FastCGI sent in stderr: "PHP message: [WHMCS Application] ERROR: WHMCS\Exception: Could not determine admin user id in /var/www/html/xxx.com/vendor/whmcs/whmcs-foundation/lib/Installer/Composer/ComposerJson.php:0 Stack trace: #0 /var/www/html/xxx.com/vendor/whmcs/whmcs-foundation/lib/Admin/Controller/HomepageController.php(0): WHMCS\Admin->hasPermission('Update WHMCS') #1 [internal function]: WHMCS\Admin\Controller\HomepageController->index(Object(WHMCS\Http\Message\ServerRequest)) #2 /var/www/html/xxx.com/vendor/middlewares/utils/src/CallableHandler.php(26): call_user_func_array(Array, Array) #3 /var/www/html/xxx.com/vendor/middlewares/fast-route/src/FastRoute.php(96): Middlewares\Utils\CallableHandler::execute(Array, Array) #4 /var/www/html/xxx.com/resources/views/admin/assent/shared/data-eula.php(0): Middlewares\FastRoute->process(Object(WHMCS\Http\Message\ServerRequest), Object(Middlewares\Utils\Delegate)) #5 /var/www/html/xxx.com/resources/views/admin/assent/shared/data-eula.php(0): WHMCS\Route\" while reading response header from upstream, client: 192.0.0.192, server: xxx.com, request: "GET /admin/index.php?rp=/admin/ HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "www.xxx.com"

I'm using nginx as webserver

Edited September 23, 2019 by Executable