I can't seem to send an identifier over a request body to Firebase from a Swift iOS app.

My javascript code works (I tested it in an API builder):

exports.numberOfVideos = functions.https.onRequest((request, response) => {
var attributionID = request.body.data.attributionID || "No attributionID found.";
functions.logger.info('[LOG]: request.body has a value of ' + JSON.stringify(request.body), {structuredData: true});
var db = admin.firestore();

db.collection("content").get().then(snapshot => {
    var total = 0;
    snapshot.forEach(doc => {
        if (doc.data().attributionID == attributionID) {
            total++;
        }
        // stuff = stuff.concat(newelement);
    });
    response.send('{"data": {"attributionID": "' + attributionID + '", "numberOfContents": "' + total + '"}}');
    return "";
}).catch(reason => {
    response.send(reason)
})
 });

My Swift code can't see to convey the data:

static func getContentCount(for obj: Object, completion: @escaping (_ count: Int?) -> Void) {
    let httpsCallable = functions.httpsCallable("numberOfVideos")

//        httpsCallable.setValue("application/json", forKey: "Content-Type")
    httpsCallable.call(["attributionID" : obj.id]) { result, error in
        if let error = error as NSError? {
            if error.domain == FunctionsErrorDomain {
                let code = FunctionsErrorCode(rawValue: error.code)
                let message = error.localizedDescription
                let details = error.userInfo[FunctionsErrorDetailsKey]
                print(error)
            }
        }
        

        if let response = result?.data as? [String: [String: Any]] {
            if let data = response["data"] {
                if let countAsAString = data["numberOfContents"] as? String {
                    let count = Int(countAsAString)
                    if count != nil {
                        completion(count)
                    } else {
                        print("Data is valid but no count found: \(result?.data)")
                        completion(nil)
                    }
                }
            }
        } else {
            print("Data is invalid: \(result?.data)")
            completion(nil)
        }
    }
}

When it worked from a REST API tester, here was the body:

POST /numberOfVideos HTTP/1.1
Host: *****************
Content-Type: application/json
Content-Length: 49

{"data":{"attributionID":"biNiaWVtmjUKoTQ1fTZu"}}

Any help would be appreciated!