It looks ilke you have two certificates in your keychain (Koot Software Design and Mac Developer: C.J. Koot (MFNVQX3C9R)) which match your search term “Koot Software Design”. You can either delete one of those certificates or supply a more specific search term.
One option here is to supply a SHA-1 hash of the specific certificate you want to use. The
codesignman page has the details.
You can see the SHA-1 hash of a certificate in Keychain Access. Double click the certificate and scroll to the bottom. You’ll find a section labelled Fingerprints, which contains SHA-1 and MD5 hashes of the certificate.
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"
After some search I finally found the solution. I had to put the certificate between brackets