not receiving push notification

Question

hi

i impelimented app42 push notification and recieve on android devices succesfully but after few days is not receive push notification.

i checked the push logs is showing below error:

"Push Android Worker Exception : com.google.android.gcm.server.InvalidRequestException: HTTP Status Code: 401"

 

later change the key on google cloud messenging credential and update key on push setting but problem exist yet.

please help me to slove this problem

thanks