Error "the GET method is not supported for this route. Supported methods: POST."

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PHP

HTML5

Hello. I've been struggling to find the way to resolve this error since I'm new to Laravel. Here is my code:

The form in buy.blade.php:

<form action="{{ route('purchase'}}" method="post" role="form">
     {{ csrf_field() }}
         <h3 class="registration-title">Registration Form</h3>
             <div class="form">
                  <div class="form-group">
                       <div class="form-wrapper-1">
                            <label for="">First Name</label>
                            <input type="text" class="get-name-1">
                       </div>
                  <div class="form-wrapper-1">
                       <label for="">Last Name</label>
                       <input type="text" class="get-name-2">
                  </div>
             </div>
                  <div class="form-wrapper-2">
                       <label for="">Email</label>
                       <input type="text" class="form-control">
                  </div>
                  <div class="form-wrapper-2">
                       <label for="">Credit Card</label>
                       <input type="password" class="form-control">
                  </div>
                  <div class="form-wrapper-2">
                       <label for="">Password</label>
                       <input type="password" class="form-control">
                  </div>
                  <div class="checkbox">
                       <label>
                            <input type="checkbox"> I accept the Terms of Use & Privacy Policy.
                                
                            </label>
                       </div>
                  </div>
                    <button class="register-button" onclick="location.href='{{'submit'}}'">Register Now</button>
                </form>

The route (web.php):

Route::post('/buy',function()
{
    return view('Buy.buyrope');
});
Route::post('submit','InputStreamReader@save')->name('purchase');

The functions in Controller InputStreamReader:

public function save(Request $request)
    {
        print_r($request->input());
        $customer = new Customers();
        $customer->First_Name = $request->First_Name;
        $customer->Last_Name = $request->Last_Name;
        $customer->Email = $request->Email;
        $customer->Credit_Card = $request->Credit_Card;
        $customer->Password = $request->Password;
        echo $customer->save();
    }

So I want to navigate from the site "localhost/merchant" to "localhost/buy" if a button is clicked. But when clicking the button to navigate to "buy.blade.php", I obtain an error

The GET method is not supported for this route. Supported methods: POST.

What I have tried:

I also changed from get to post but it still pops out the same error and it's been several days I couldn't fix this bug and I even did like what some sites say about this error but nothing changed. Please help me. I still don't fully understand the route and navigate mechanics in Laravel 8.