How to add Notification Service Extension for Firebase?

I am trying to follow the guide here: https://firebase.google.com/docs/cloud-messaging/ios/send-image

I went to New > Target > Notification Service Extension (embedded this new target into the original target) and pasted in NotificationService.m:

@interface NotificationService ()

@property (nonatomic, strong) void (^contentHandler)(UNNotificationContent *contentToDeliver);
@property (nonatomic, strong) UNMutableNotificationContent *bestAttemptContent;

@end

@implementation NotificationService

- (void)didReceiveNotificationRequest:(UNNotificationRequest *)request withContentHandler:(void (^)(UNNotificationContent * _Nonnull))contentHandler {
    self.contentHandler = contentHandler;
    self.bestAttemptContent = [request.content mutableCopy];

    // Modify the notification content here...
    self.bestAttemptContent.title = [NSString stringWithFormat:@"%@ [modified]", self.bestAttemptContent.title];

    // Call FIRMessaging extension helper API.
    [[FIRMessaging extensionHelper] populateNotificationContent:self.bestAttemptContent
                                             withContentHandler:contentHandler];

    self.contentHandler(self.bestAttemptContent);
}

- (void)serviceExtensionTimeWillExpire {
    // Called just before the extension will be terminated by the system.
    // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
    self.contentHandler(self.bestAttemptContent);
}

@end

I am now getting Use of undeclared identifier 'FIRMessaging' in NotificationService.m.

In NotificationService.m I tried to import similarly to my original target's AppDelegate.m where FIRMessaging is available and working with no issues:

#import "NotificationService.h"
#import <Firebase.h>
#import "RNFirebaseNotifications.h"
#import "RNFirebaseMessaging.h"
...

Then I get 'Firebase.h' file not found. I am confused because it seems to work in the original target, and this notification service extension is embedded in that target. I have tried messing with Header Search Paths and Framework Search Paths without much luck. What am I doing wrong?