Error 405 when android push notification

My app is on Google Play already. Push notification was working well.
But now I’m getting 405 error code when sending push notification.

" Mismatched Sender ID. A registration token is tied to a certain group of senders. When a client app registers for GCM, it must specify which senders are allowed to send messages. You should use one of those sender IDs when sending messages to the client app. If you switch to a different sender, the existing registration tokens won’t work."

What is wrong ?

regards.

What service are you using to send the push notification?

I’m using ionic.io web interface to send, in “one-time” link .

Changed anything here (see step 2 at the bottom)?

Which step? where ? Change what ?

Sorry, forgot the link:

I meant:

ionic config set gcm_key