To enable this provider, you need to enable fcm-xmpp-api bean within push component configuration scope.

Example. 

push () {
    'fcm-xmpp-api' () {
        # FCM configuration here
    }
}

FCM XMPP API provider will not work properly without API key and project id as this values are required for authorization by FCM. You need to get information from FCM account.

When you have this data, you need to pass sender id as sender-id property and server key as server-key property.

Example. 

push () {
    'fcm-xmpp-api' () {
        'sender-id' = 'your-sender-id'
        'server-key' = 'your-server-key'
    }
}

By default this provider uses single client to server connection to FCM for sending notifications. If in your use case it is to small (as you need better performance), you should adjust value of pool-size configuration property. Setting it to 5 will open five connections to FCM for better performance.

Example. 

push () {
    'fcm-xmpp-api' () {
        'pool-size' = 5
    }
}