You can retrieve specific details of a logged-in client in WHMCS by using {client.x} in fields.

• firstname: The first name of the client.
• lastname: The last name of the client.
• fullname: The full name of the client (combination of first and last name).
• companyname: The name of the company associated with the client.
• email: The email address of the client.
• address1: The first line of the client’s address.
• address2: The second line of the client’s address.
• city: The city name in the client’s address.
• fullstate: The full name of the state in the client’s address.
• state: The abbreviation or code of the state in the client’s address.
• postcode: The postal code or ZIP code in the client’s address.
• countrycode: The country code associated with the client’s address.
• phonenumber: The client’s phone number.
• countryname: The name of the country associated with the client’s address.
• phonenumberformatted: The formatted version of the client’s phone number.
• tax_id: The tax identification number associated with the client.

Example usage: If you want to display the logged client’s first name in a text field you need to click on text element and then select advanced tab and put this code in default value:

{client.firstname}

This will automatically fill text input value to “John” if the client’s first name is “John”.