I am not able to access the cross site lists using REST API in SharePoint Designer 2013 Workflow. I am making a call using action "Call HTTP Web Service". I am facing the error in responseCode variable like "Forbidden".
You need get the return
d.GetContextWebInformation.FormDigestValue from restapi
/_api/contextinfo and insert the value on header
https://blog.appliedis.com/2014/10/09/sharepoint-designer-2013-workflow-working-with-web-services/ has a really good guide on setting up the security contexts you need. Too long to post here.
Not much experience with Designer workflows as I usually work with Visual Studio but... Might it be a permission issue? If so try using an app step and activate the "Workflow can use app permissions" feature. More about this: https://docs.microsoft.com/en-us/sharepoint/dev/general-development/create-a-workflow-with-elevated-permissions-by-using-the-sharepoint-workflo
Don't know if you are trying to read or write data but the X-RequestDigest from context info is not needed for read operations.