Error sending push to gateway (not authorized)


I am using external gateway to handle my push notification but in logs i see this

{"level":40,"time":"2023-08-21T10:38:33.284Z","pid":25013,"hostname":"chat","name":"Push","msg":"Error sending push to gateway (not authorized) '{\"detail\":\"Given token not valid for any token type\",\"code\":\"token_not_valid\",\"messages\":[{\"token_class\":\"AccessToken\",\"token_type\":\"access\",\"message\":\"Token is invalid or expired\"}]}'"} 

Server Setup Information

Version: 6.2.9
Apps Engine Version: 1.39.1
Node Version: v14.21.2
Database Migration: 294 (July 7, 2023 5:54 PM)
MongoDB: 5.0.15 / wiredTiger (oplog Enabled)

is there any guide to setup the gateway as required by rocket chat?