Cannot connect via SQL Server Management Studio into SSIS ?

Hello finished installing/adding SQL Server Integration Services 2016 using the [NT Service\MsDtsServer130] account.

One of our non departmental consultants using their out of dept Doman account is getting the following error when trying to connect to SSIS via SQL Server Management Studio:

[Cannot connect to ServerName.

Failed to retrieve data for this request. (Microsoft.SqlServer.Management.Sdk.Sfc)

Exception from HRESULT: 0XC00160AD (Microsoft.SqlServer.DTSRuntimeWrap)

Exception from HRESULT: 0XC00160AD (Microsoft.SqlServer.DTSRuntimeWrap)]

I tried the following link http://dinesql.blogspot.com/2016/07/connecting-to-integration-services-access-is-denied.html but this contractor's outside Domain doesn't show up to add his Domain account.

Anything else can be done and/or needs adjusting?

Thanks in advance.