Function call not working with AI chatbot

I am trying out sendbird for its Chatbot AI. One of my use cases is to trigger a function call on AI detection, however, as soon as I enable the function call the whole AI chatbot stops working (for any query). It returns the following error:

Unexpected error has occurred. Try again and contact customer support if the issue persists.

I also checked the bot log and didn’t find anything helpful. Note that I am currently trying out the product so still on free tier.