Unable to get the firebase token in Android 7

Ionic Framework
1

I have installed Cordova: https://github.com/chemerisuk/cordova-plugin-firebase-messaging plugin to handle the notification. It’s working fine in android 9 but when I test the application in android 7 it’s not getting the token from firebase.

               this.firebaseMessaging.getToken().then((token) => {
                    alert(token);
                    this.api.updateToken(token).then((res) => {
                    }, (err: any) => {
                    });
                }).catch((res)=>{
                    console.log(res);
                });

same code working fine for android 9 but not in android 7.

can anyone tell me what seems to wrong?