I found this: Specifying a wrong template name will result in this issue.
So I think it might be that just a wrong template name or not finding the template is the issue.
I renamed my template from "File Web Page" to "webpage" and it worked - might also did have some newline before.
@Matthew: Could a better error message like "Could not find template" help here?
For me it also does not work.
Error message via popup in my shortucts:
"The operation couldn't be complete. (InterchangeCall-backErrorDomain error 0.)" - OK
Just copied from here:
(linked from there: https://www.icloud.com/shortcuts/c18e9836d08c4e528e7a0ed6a472910b)
Maybe I should do the shortcut myself? Not sure if the shortcuts are all compatible between IPhones?!
Could you share the shortcut you are using and I'll take a look and try and reproduce your issue (or a screenshot)