Publishing changes from background threads is not allowed

This is the error I got,

Publishing changes from background threads is not allowed; make sure to publish values from the main thread (via operators like receive(on:)) on model updates.

Here is the code,

class AdsViewModel: ObservableObject{
    @Published var ads: [AdPost]?
    
    @Published var alertMessage = ""
    @Published var showAlert = false
    
    @Published var createAd = false
    @Published var isWriting = false

    func fetchAdPosts() async {
        do{
            let db = Firestore.firestore().collection("Ads")
            
            let ads = try await db.getDocuments()
            

            DispatchQueue.main.async {
                self.ads = ads.documents.compactMap({ ad in
                    return try? ad.data(as: AdPost.self)
                })
            }
            
        }
        catch{
            
            self.alertMessage = error.localizedDescription
            showAlert.toggle()
        }
    }
}