'powershell signing certificate unknownerror

I am following the instructions to sign a script

and I've got to the part where I sign the add-signature.ps1 file so that I can sign my script using it

$cert = @(Get-ChildItem cert:\CurrentUser\My -codesigning)[0]
Set-AuthenticodeSignature add-signature.ps1 $cert

and I get this error:

I've Googled endlessly but found no solutions! I'm running PS in Administrator mode and I've set the policy for CurrentUser to AllSigned

Can anyone help me? Do I need to set all the policies to AllSigned?

UPDATE: Deleting all the Certs and starting again, following the Microsoft instructions: and of course I get an error when I try to run the add-signature.ps1 script - help!

Solution 1:^[1]

Importing the cert to \CurrentUser\Root as well as TrustedPublisher worked

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Source: Stack Overflow

Solution	Source
Solution 1	Ryan M

'powershell signing certificate unknownerror

Solution 1:[1]

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Solution 1:^[1]