Sometimes apps leave behind coding that can interfere with other apps. This applies to even after you have removed the App from your store.
In particular the Product Booking app leaves behind some code that interferes with BookThatApp collecting the booking details. The easiest way to identify if code is remaining is to view your browser's developer tools by selecting F12 or right-clicking your mouse and selecting Inspect.
You should see an error similar to below when you select the Console tab.
Here are the steps to resolve the issue.
1. Open the affected product in your Shopify admin.
2. In the product description section click the
<> button to go into HTML source mode. It will look similar to the below.
3. Remove the line following line from the bottom:
5. Repeat the process for all other products that were configured in the Product Booking app.