Laravel Queue Job Error Object of class Illuminate\\Queue\\Jobs\\DatabaseJob could not be converted to string

I am using a Laravel Database Queue to send a email UnAssignedMail

$data = array('user' => $user_admin->toArray(), 'var1' => 'Test','teamName' => $teamName,'expertise' => $expertise);
UnAssignedMail::dispatch($data);

When I run the php artisan queue:work It is processing without any syntax error. In the log when I check

2021-02-09 02:31:09] local.ERROR: Object of class Illuminate\Queue\Jobs\DatabaseJob could not be converted to string {"exception":"[object] (Error(code: 0): Object of class Illuminate\\Queue\\Jobs\\DatabaseJob could not be converted to string at D:\\laragon\\www\\domain\\vendor\\laravel\\framework\\src\\Illuminate\\Database\\Connection.php:582)
[stacktrace]
#0 D:\\laragon\\www\\domain\\vendor\\laravel\\framework\\src\\Illuminate\\Database\\Connection.php(582): PDOStatement->bindValue(2, Object(Illuminate\\Queue\\Jobs\\DatabaseJob), 2)