Integration with external APIs

Hello! I want to create a WhatsApp bot based on an assistant who will play the role of a flower sales manager (for example). I have an external API that I want this assistant to integrate with. Tell me, is this possible? I was able to solve this problem by creating an assistant in the chatgpt interface (in the actions I described the API scheme and the necessary instructions). But for some reason I can’t do the same for an assistant created using the openai API…