So, the way I’ve ended up doing this is as follows. It’s probably not the optimal way but I can’t find a way to change the submission data during the submission workflow (the redirect action always seems to read the original entered data). Basically, the key hook is ninja_forms_run_action_settings where you can filter $action_settings which contains the redirect url.
In my Action class:
class CustomProcessing extends NF_Abstracts_Action {
private string $_redirect_url;
public function __construct()
{
parent::__construct();
$this->_nicename="Custom Process";
add_filter( 'ninja_forms_run_action_settings', [ $this, 'changeRedirectURL' ], 10, 4 );
}
public function process( $action_id, $form_id, $data ) {
// code to call API endpoint
// set redirect url on response from API
if ( 201 === $response[ 'response' ][ 'code' ] ) {
$this->_redirect_url = $body_url;
}
return $data
}
public function changeRedirectURL( $action_settings, $form_id, $action_id, $form_settings )
{
if ( '<redirect action name>' === $action_settings[ "label" ] ) {
$action_settings[ 'redirect_url' ] = $this->_redirect_url;
}
return $action_settings;
}
}