<?php

use GeneaLabs\LaravelMixpanel\Http\Controllers\StripeWebhooksController;
use Illuminate\Support\Facades\View;

Route::controller('genealabs/laravel-mixpanel/stripe', StripeWebhooksController::class);

<?php

use GeneaLabs\LaravelMixpanel\Http\Controllers\StripeWebhooksController;
use Illuminate\Support\Facades\View;

Route::post('genealabs/laravel-mixpanel/stripe', ['uses' => 'GeneaLabs\LaravelMixpanel\Http\Controllers\StripeWebhooksController@postTransaction']);

Resolve routing depreciation in Laravel v5.3
Resolve routing depreciation in Laravel v5.3

This will remove the Route::controller() call and replace it with an explicit route call.