Android device only receive 1 notification when offline.

My app sends non-collapsible push notification.
When push notification are sent while device is online, everything works fine. Notifications are sent one by one. The problem is that if the device is offline (closed or airplane mode) only the last notification sent is received when the device come back online.

A work around that seems to be popular online is to generate unique collapseKey to force firebase to push notification in separate "collapse group".
I know the limit is only 4 collapse key, but it is enough notifications for the app I'm building.

I've achieved the desired result on IOS by settings my apns-collapse-id to a random UUID for each notifications but now that I'me trying with android it doesn't seems to work.

I uses
Firebase-admin version 9.1.1
```

com.google.firebase
firebase-admin
9.1.1

```
This library uses FCM HTTP v1 endpoint

The collapseKey fields works.
When setting it with this function : `AndroidConfig.builder().setCollapseKey("non_unique_collapse_key").build()`

The notifications are overwritten.

If I set it like this : `AndroidConfig.builder().setCollapseKey(UUID.randomUUID().toString()).build()`

All notification are sent separately.

The problem is that if I put my android to airplane mode, send myself 3 notifications (with 3 different collapse_key)
When I put my device back online, I only receive the last notification sent.

The same cannot be said for IOS.

I set my notification like so :
```
ApnsConfig.builder().putHeader("apns-collapse-id", collapseKey)
.setAps(Aps.builder().setAlert(
ApsAlert.builder().setTitle(title).setBody(notificationContent).build()).build())
.build();
```

and when I put my iphone back online, I receive 3 notifications.

从 AndroidConfig.builder().setCollapseKey 的使用方式以及 issue 中描述的 Firebase Admin Java SDK 9.1.1 配置开始。让 Android 设备处于飞行模式，通过 FCM HTTP v1 端点发送三个具有不同折叠键的通知来复现，然后将结果与 APNs 配置进行比较。完成标准是确定 Android 的送达行为是否符合预期，或确认一个有文档记录的 SDK 或 FCM 问题。

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