When it looks like devices haven't successfully received messages, CHECK first for these two potential causes:

Foreground message handling for notification messages. Client apps need to add message handling logic to handle notification messages when the app is in the foreground on the DEVICE. See the DETAILS for iOS and Android.

Network firewall restrictions. If your organization has a firewall that restricts the traffic to or from the Internet, you need to configure it to ALLOW connectivity with FCM in order for your Firebase Cloud Messaging client apps to receive messages. The ports to open are:

• 5228
• 5229
• 5230

FCM usually uses 5228, but it sometimes uses 5229 and 5230. FCM does not PROVIDE specific IPs, so you should allow your firewall to accept outgoing connections to all IP addresses contained in the IP blocks listed in Google's ASN of 15169.

When it looks like devices haven't successfully received messages, check first for these two potential causes:

Foreground message handling for notification messages. Client apps need to add message handling logic to handle notification messages when the app is in the foreground on the device. See the details for iOS and Android.

Network firewall restrictions. If your organization has a firewall that restricts the traffic to or from the Internet, you need to configure it to allow connectivity with FCM in order for your Firebase Cloud Messaging client apps to receive messages. The ports to open are:

FCM usually uses 5228, but it sometimes uses 5229 and 5230. FCM does not provide specific IPs, so you should allow your firewall to accept outgoing connections to all IP addresses contained in the IP blocks listed in Google's ASN of 15169.