underlyingCoreCryptoError(error: -1) while verify signature

Question

getting error while verifying private key signature using cryptokit

What i tried:

func signMessage(_ message: String, withPrivateKey privateKey: Data) -> Data {
    do{
        let key = try P256.Signing.PrivateKey(rawRepresentation: privateKey) // here it throws error
        let signature = try key.signature(for: message.data(using: .utf8)!)
        return signature.rawRepresentation
    }catch{
        print(error)
        return Data()
    }
}

Error: underlyingCoreCryptoError(error: -1)

Additional Info: message is kind of header token and looks like this

eyJhbGciddJFUzI1diIsImtpZdI6IjdXNFQ5dlFRdEMifQ==.eyJpYXQiOjE2Off5MTEwOfksImlzcyI6fjdWUTfQOExRfFMifQ==

should i need to trim message with =?

i am not sure what's wrong with this code but it throws underlyingCoreCryptoError. Suggestion will be thankful.