Hi @recoildesign
Thanks for the explanation.
In this case, I suggest you create the new post by using the acf_form()
function. To learn how to create a new post, kindly check this page: https://www.advancedcustomfields.com/resources/using-acf_form-to-create-a-new-post/.
You can modify the saving process by using the acf/save_post hook and use the third-party API in this hook. That way you can modify the post data by using the data from the API.
I hope this helps 🙂