Generally, this happens when the text and the background color on iframe are set to white due to which the text is not getting displayed. You can try selecting the text on the sign-up/login page to confirm the same.
Please refer to the screenshot below:
In such cases, it is suggested to change the color of the text to resolve the issue.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)