Can you provide more context?
What happens when you use the Populate text field on web page action? Does it fail an throw an error? Does it succeed without any errors, but does not actually populate the text field? If it fails, can you share the error message?
Also, can you try to right-click the text field in your browser and select "Inspect"? This will show you the selector for the field in the browser developer tools. Please share a screenshot of that.
Please also include a screenshot of the web UI element you have captured in PAD.
This will help us help you figure out the problem and resolve it.