Kartra doesn’t currently have an API method for listing all of the custom fields in your account. To get around this, we query the first lead in your account, and build the list of available custom fields based on fields found on that lead.
If you’re missing custom fields in WP Fusion, or if you’ve just added a custom field in Kartra, try adding some data to the custom field for the first lead in your Kartra account, then resynchronize the available fields by going to Settings » WP Fusion » Setup, and clicking the green Resynchronize button.
Register the fields in WordPress
WP Fusion also lets you type a field name directly into the fields select dropdown.
If you’re still not able to get your Kartra fields to load, you can type the merge field for the custom field into the dropdown, and hit enter when it prompts “(new)”.