firebase-ios-sdk: InAppMessaging - Failed restful api request to fetch in-app messages 400

[READ] Step 1: Are you in the right place?

yes

[REQUIRED] Step 2: Describe your environment

• Xcode version: 10.1
• Firebase SDK version: 5.20.0
• Firebase Component: InAppMessaging + InAppMessagingDisplay
• Component version: 5.20.0

[REQUIRED] Step 3: Describe the problem

We have been using Firebase since some years. Everything works so we are confident that our setup is working correctly. Currently we are using Messaging, RemoteConfig, Performance components.

We are adding InAppMessaging component into the app. We see this messages in console:

5.20.0 - [Firebase/InAppMessaging][I-IAM130004] Failed restful api request to fetch in-app messages: seeing http status code as 400 with body as {
  "error": {
    "code": 400,
    "message": "Request contains an invalid argument.",
    "status": "INVALID_ARGUMENT"
  }
}

5.20.0 - [Firebase/InAppMessaging][I-IAM700002] Error happened during message fetching Error Domain=NSURLErrorDomain Code=400 "(null)"

Steps to reproduce:

Just add InAppMessaging + InAppMessaingDisplay. We add the framework manually by dragging them into Xcode and copy the InAppMessagingDisplayResources.bundle in build phase.

Relevant Code:

No code was added since the tutorial said so.