Failed to connect to source portal

Error Message

Attempting to use the ArcGIS Solutions Deployment tool in ArcGIS Pro returns the error message:

Error:   
Failed to connect to source portal

Occasionally, the following error message is also returned:

Error:   
Failed to add <name of solution>

Cause

A proxy server or firewall is blocking the connection to ArcGIS Online.

Solution or Workaround

To resolve the issue:

1. Navigate to Control Panel > Network and Internet > Internet Options. The Internet Properties window opens.
2. Select the Security tab.
3. Click Trusted Sites > Sites.
4. Add the following domains to the list, individually:

*.arcgis.com
*.arcgisonline.com
*.amazonaws.com
*.virtualearth.net
*.esri.com

5. Click Close > OK.

Note:
In some organizations, the IT team may also need to allow the domains in Step 4 on the organization's proxy server and/or firewall.