One of my customers wanted to use Zenler as an all-in-one platform and gave up after 2 months. For another customer, we can only use Zenler because we handle all billing and marketing via WooCommerce and ActiveCampaign. Zenler has translation problems in some places and is still struggling with reliability issues. Also, not all payment methods that customers in German-speaking countries are used to are connected. If this is not a problem with the payment options, you could consider using Kajabi. This offers a reliable marketing solution and can be used via Zapier with German billing tools such as Fastbill or you can use Stripe's billing function. Of course, all of this depends on exactly what kind of platform you want to build, i.e. how many people participate, what revenue you generate, etc. I currently find a WordPress-based solution with LearnDash and the deep integration with ActiveCampaign via WP Fusion to be a very good solution. This can also map 1:1 coaching.