If you are getting KCB M-pesa activation error "Failed. The transaction cannot be completed now. Try again later", then try to update your Mpesa Menu.
To update mpesa menu then go to Mpesa>My Account>Update Customer menu>enter your Mpesa pin. After completing the mpesa menu update, go back to KCB Mpesa and try activating.
If the update fails you need to visit the nearest Safaricom shop to upgrade your SIM card to the new generation