Why the SDK always gave 401 errors even though the API Key is right?

Android SDK version: 10.4.2

iOS SDK version: 10.3.4

Few days ago since I posted this, the SDK worked fine, and then about two days ago, it suddenly stopped working for unknown reason. We didn't even change the implementation code. The Messenger screen always stuck with "Something wrong happened. Please try it again.". Pressing "Reload" didn't help as well.

When initializing the app, there was no error. After registering the user through an User ID and setting the FCM Token, also showed no errors. Once we got to the part to update the User or turning on the Messenger screen, then we received this error.

This error is the example during turning on the Messenger. Updating the user also showed similar error message.

ERROR - Tried to get conversations for display in the conversations list but there was a network error (401) - Request failed: unauthorized (401)

There's no way the API key used was wrong. If it worked previously without changes, why did it stop working and returned errors that indicate something might be wrong with the API Key?