Myfitnesspal app redirects to web page but I created account with Apple ID

Hi, I just bought premium myfitnesspal and wanted to connect it to my smart weight scale. I found the scale app in a list of apps in myfitnesspal, clicked on it and then it redirected me to a myfitnesspal website to log in. But I don't have any password I can fill in because my account in the actual app was created with Apple ID (and I hid my email address). So I only have that alphanumeric email address that I can fill in as username but there's no password in the Passwords app that I can use to continue.

How do I go about this without loosing access to the overly expensive premium account?

I found this older post, presumably about the same issue but the response in it doesn't help: myfitnesspal web id when I loaded the app… - Apple Community

Thanks a lot!