React Native gives you three paths. Pick the one matching your project shape, and if you're an Expo user, read the callout below carefully because there's exactly one trap you need to avoid.

Bare RN with @react-native-firebase/messaging

import messaging from "@react-native-firebase/messaging";

export async function setupPush() {
  const status = await messaging().requestPermission();
  if (
    status === messaging.AuthorizationStatus.DENIED ||
    status === messaging.AuthorizationStatus.NOT_DETERMINED
  ) return;

  const fcmToken = await messaging().getToken();
  await sendTokenToServer({ platform: "fcm", token: fcmToken });

  messaging().onTokenRefresh((newToken) => {
    sendTokenToServer({ platform: "fcm", token: newToken });
  });
}

Expo (managed or bare) with expo-notifications

import * as Notifications from "expo-notifications";

export async function setupPush() {
  const { status } = await Notifications.requestPermissionsAsync();
  if (status !== "granted") return;

  // DEVICE token = native APNs hex / FCM token (use this with edgepush)
  // EXPO token = "ExponentPushToken[...]" (only Expo's Push Service)
  const token = await Notifications.getDevicePushTokenAsync();

  await fetch("https://your.api/register-token", {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      platform: token.type,
      token: token.data,
    }),
  });
}