Unified SDK not working in iOS

I have implemented the Unified SDK as instructed in the documentation and also on the sample app provided.

Initializing all parts seem to work fine since no error is thrown, and the view controller is built and presented successfully.

Init calls (keys are redacted):

ZendeskCoreSDK.Zendesk.initialize(appId: "", clientId: "", zendeskUrl: "")
SupportProvidersSDK.Support.initialize(withZendesk: ZendeskCoreSDK.Zendesk.instance)
AnswerBot.initialize(withZendesk: ZendeskCoreSDK.Zendesk.instance, support: SupportProvidersSDK.Support.instance!)
Chat.initialize(accountKey: "")

Build UI calls:

let answerBotEngine = try AnswerBotEngine.engine()
let supportEngine = try SupportEngine.engine()
let chatEngine = try ChatEngine.engine()
let sessionViewController = try Messaging.instance.buildUI(engines: [answerBotEngine, supportEngine, chatEngine], configs: [messagingConfiguration])

I have a valid flow saved, but it doesn't really load - not even the first item in the flow. Right off the bat, it says: "Uh-oh. Sorry, something's up. I can't answer questions right now."

Then it offers to leave a message or chat to an agent. If I choose "leave a message" it says "Something went wrong and I wasn't able to send your message. Please try again later."

What would be possible reasons for this?