How to implement custom action that require pub.dev import?

I am having trouble implementing this custom action that will launch an onboarding URL by using a generated SDK from Phyllo api. I had follow various guide on how to implement it but unable to do so. I also added pubspec dependencies as required in pub.dev guide. I am unsure what can I do to make it work, I would appreciate anyone who could help.

Here is the docs of the SDK integration of Phyllo:
https://docs.getphyllo.com/docs/api-reference/connect-SDK%2Fmobile%2Fflutter-SDK-integration

Here is the pub.dev guide: https://pub.dev/packages/phyllo_connect

Below is the code I had added into the custom action:

// Automatic FlutterFlow imports
import '/backend/backend.dart';
import '/backend/schema/structs/index.dart';
import '/flutter_flow/flutter_flow_theme.dart';
import '/flutter_flow/flutter_flow_util.dart';
import '/custom_code/actions/index.dart'; // Imports other custom actions
import '/flutter_flow/custom_functions.dart'; // Imports custom functions
import 'package:flutter/material.dart';
// Begin custom action code
// DO NOT REMOVE OR MODIFY THE CODE ABOVE!

import 'package:phyllo_connect/phyllo_connect.dart';

final PhylloConnect _phylloConnect = PhylloConnect.instance;
Future launchSdk(
  String? clientDisplayName,
  String? userId,
  String? token,
) async {
  // Add your function code here!
  void launchSdk(String workPlatformId) {
    Map<String, dynamic> config = {
      'clientDisplayName': clientDisplayName,
      'environment': PhylloEnvironment.staging.name,
      'userId': userId!,
      'token': token!,
      'workPlatformId': workPlatformId
    };

    _phylloConnect.initialize(config);
    _phylloConnect.open();
  }
}