Laravel: Replacing middleware parameters in nested routes

I have a Route group which applies middlewares to all nested routes. I am passing a parameter to it.

Inside the group, though, I have a specific route for which I want to pass a different parameter. Which I do as following:

Route::group(['prefix' => '/' . $languagePrefix, 'middleware' => ['sessionapi', 'abtest:0']], function () {

// other routes

Route::get('/i18n', [
    'as' => 'api:i18n',
])->middleware('abtest:1');

}

But in the middleware handle itself, the parameter is always 0, the generic one, even if I visit the route with the different parameter.

How come?

public function handle($request, \Closure $next, string $customPar = null)
{
    // ...
    dd($customPar); // always 0
    // ... 
}

I tried to use ->withoutMiddleware(['abtest'])->->middleware('abtest:1') but it didn't work

You can't replace abtest:0 middleware. Because, it had executed first. So you must change your route structure

Route::group(['prefix' => '/' . $languagePrefix, 'middleware' => ['sessionapi']], function () {
    Route::middleware('abtest:0')->group( function(){
            // all routes using abtest:0
    });

    Route::get('/i18n', [
        'as' => 'api:i18n',
    ])->middleware('abtest:1');


});