If you are on an IFrame integration with zingfit, and your customer is telling you they cannot log in, it is possible their browser setting is preventing them from doing so.
If a customer's website is set to Block All Cookies in their browser, no website will work. This is not a zingfit issue but a common browser requirement.
If the customer is attempting to log in, but can't please advise them to un-check 'Block all cookies' in their settings. Doing so will allow the customer to proceed with the login process.