How do I trigger a OneSignal push notification on a new follow event in Swift?

I'm a new developer with an iOS app that uses OneSignal for push notifications and Firebase for the database. I want to send a push notification to a specific user when they get a new follow, but I'm not sure how to implement it.

Below are my current code snippets:

SWIFTCopied
static func follow(uid: String) async throws {
        guard let currentUid = Auth.auth().currentUser?.uid else { return }
        
        let userFollowingDoc = FirestoreConstants.FollowingCollection.document(currentUid).collection("user-following").document(uid)
        let userFollowersDoc = FirestoreConstants.FollowersCollection.document(uid).collection("user-followers").document(currentUid)
        
        try await Firestore.firestore().runTransaction { transaction, errorPointer in
            do {
                let userDoc = FirestoreConstants.UserCollection.document(uid)
                let currentUserDoc = FirestoreConstants.UserCollection.document(currentUid)
                
                transaction.updateData(["stats.followers": FieldValue.increment(Int64(1))], forDocument: userDoc)
                transaction.updateData(["stats.following": FieldValue.increment(Int64(1))], forDocument: currentUserDoc)
                
                transaction.setData([:], forDocument: userFollowingDoc)
                transaction.setData([:], forDocument: userFollowersDoc)
            } catch {
                errorPointer?.pointee = error as NSError
                return nil
            }
            return nil
        }
    }

import UserNotifications
import OneSignalExtension

class NotificationService: UNNotificationServiceExtension {
    
    var contentHandler: ((UNNotificationContent) -> Void)?
    var bestAttemptContent: UNMutableNotificationContent?
    var receivedRequest: UNNotificationRequest!
    
    override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
        self.contentHandler = contentHandler
        self.receivedRequest = request
        bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)
        
        guard let bestAttemptContent = bestAttemptContent else { return }
        
        // Configure the notification content
        OneSignalExtension.didReceiveNotificationExtensionRequest(
            self.receivedRequest,
            with: bestAttemptContent,
            withContentHandler: contentHandler
        )
        
        // Add custom notification handling if needed
        if let userInfo = bestAttemptContent.userInfo as? [String: Any] {
            // Example: Add a custom category for follow notifications
            if let notificationType = userInfo["type"] as? String, notificationType == "follow" {
                bestAttemptContent.categoryIdentifier = "FOLLOW_CATEGORY"
            }
            
            // Example: Modify the notification body based on the type
            if let senderName = userInfo["senderName"] as? String {
                bestAttemptContent.body = "\(senderName) \(bestAttemptContent.body)"
            }
        }
        
        // Add a custom sound
        bestAttemptContent.sound = UNNotificationSound.default
    }
    
    override func serviceExtensionTimeWillExpire() {
        // Called just before the extension will be terminated by the system.
        guard let contentHandler = contentHandler,
              let bestAttemptContent = bestAttemptContent else { return }
        
        // Use this as an opportunity to deliver your "best attempt" at modified content
        OneSignalExtension.serviceExtensionTimeWillExpireRequest(
            self.receivedRequest,
            with: bestAttemptContent
        )
        
        contentHandler(bestAttemptContent)
    }
}

Any guidance on integrating OneSignal with a new follow event, or suggestions on how to structure the Cloud Function to trigger notifications would be appreciated.