The GET method is not supported for this route. Supported methods: POST. When sending html data in post request

I have a form with post method where i have 3 input fields all the input field are of text type what I'm doing is sending POST request to server for updating data. When I'm sending plain text data is being updated/stored. But When I'm trying to send html data which is given below.

<script>
 alert('Facebook Pixel Working');
</script>

throws below error

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

But When I send plain text in post request it worked for me.

Here is my route

Route::post('/dashboard/post/update-allsettings', 'DashboardController@post_update_allsettings'); 

Thanks in advance.

via Chebli Mohamed