Regarding the slash character:Element Name and Model Name cannot include the slash character (it is reserved as a path delimeter), therefore constants have an additional property, Constant Value which can include it. So what you should do is name the constant however you wish (e.g. "My URL", and enter the actual url as the value), as in the follwoing screenshot:
Regarding the validation error:Triggers and Exits (commoinly known as Slots) have a data type defined (you can see it as the Model Name in the Rename dialog, as well as the shared dataTypeId property in the Properties view.Flows (model arrows) must have the same data type at both ends, and it seems that the <Target Window> trigger is not of type Text (obviously the flow source, being a text constant is of that type). I'm guessing that what you did is that you renamed the <Replace> trigger (which is included by default in the Go to URL template, and is of type Boolean) into <Target Window> resulting in the validation error. To overcome this do either of the following:
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