Hi Henzel. Thank you for your question. You are able to integrate your 3rd party website with Sympl through the use of widgets. You can use the widgets to display the calendar availability, and/or you can use widgets to accept booking inquiries. You can then go on to manually confirm those inquiries after verifying the details with the guest. You can learn more about it in this help article here. To access widgets, just sign into the App Store to subscribe to the Website Widgets module.
In order to integrate a bookable website with Sympl, I would like to recommend Webready. You can easily create a highly customizable website in seconds, and have it ready for publication in a matter of minutes. It really depends on your desired levels of customization. With the website, you can add a booking engine that will allow you to take instant bookings that instantly reflect in your Sympl calendar, and sync to your channels.
If you want to use a custom domain with Webready, we can set you up with a free trial of the Standard Plan, so that you can benchmark your booking performance using your official domain.
Please let me know if any of these solutions work for you.