Error: getaddrinfo EAI_AGAIN

[kiancaca]

Please provide the following:

1. SDK Version: 35
2. Platforms(Android/iOS/web/all): Android & iOS

I sent push notification from backend like this:

const postExpoBackend = async (to, title, body, auctionLink) => {
  const expoURL = 'https://exp.host/--/api/v2/push/send';

  const response = await axios({
    method: 'POST',
    url: expoURL,
    data: {
      "to": to,
      "title": title,
      "body": body,
      "sound": "default",
      "data": {
        "message": auctionLink
      }
    },
    headers: { 'Content-Type': 'application/json' }
  });
}

Both iOS and Android can get the push notification the first time.
When I test it the second time, I cannot get push notifications on both phones, and gets the error code below from my backend.

Error: getaddrinfo EAI_AGAIN exp.host exp.host:443 at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:56:26)

Note: my Firebase is in Flame plan.

[kiancaca]

Also, FCM is free on three modes in Firebase (ref: Firebase Pricing), why EAI_AGAIN is caused by Spark Plan.