Does GPTs-Builder support function calling?

Would like the GPTs conversation with a client to be used to create a JSON which would then be used by an action that sends a request to an external API. Currently the JSON being created isn’t consistent. I don’t see function calling option so wondering If I missed anything?

I think you could either do that as an external API call then use a plugin to interact with it for your GPT or you can format it directly into an action.
https://platform.openai.com/docs/actions