How do I set up delegation for a group managed account?

Question

System administration

There is an IIS server that provides access to a shared folder on a file server using the WebDAV protocol. Accordingly, Kerberos and Resource Based Constrained Delegation are used. If the application pool runs under the NetworkService account, then for delegation we use the command

Set-ADComputer -Identity "FileServer$" -PrincipalsAllowedToDelegateToAccount (Get-ADComputer -Identity "IISServer$")

And what to prescribe if the pool works under the Group Managed Service Account?
Tried

Set-ADComputer -Identity "FileServer$" -PrincipalsAllowedToDelegateToAccount (Get-ADServiceAccount -Identity "WebDAVService$")

- Access denied...