final DojahFinancial _dojahFinancial = DojahFinancial(
    appId: 'xxxxxxxxxxxxxxx', //required
    publicKey: 'prod_pk_xxxxxxxxxxxxxx', //required
    type : 'custom'  //link, identification, verification, liveness, payment (required)
    amount : 100, // (optional) used for Payment widget only
    userData,    //object
    metaData,    //object (optional)
    config,  //object (optional)
    referenceId,    //NB: referenceId length must be more that 10 characters 
  );

  _dojahFinancial.open(context, onSuccess: (result) {
    print('$result');
  }, onError: (err) {
    print('error: $err');
  });

Additional information