Capturing Data on Multistep form to send to an API I am connecting to an API that returns some data based on a user's zipcode.  This data needs to be included in the payload of a second call to the API along with sone other form values.

I wanted to build the webform as a multistep, the first page collects the zip code and after the Next Page is clicked, do an API call to send the zipcode and save the response from that call, so that on the second page the Submit sends via another API call that response data plus all of the form values.

This Get the draft data in the webform hook_form_FORM_ID_alter() seems to be the answer but not quite.
You should write a custom WebformHandler that adds the return API data to $form_state and then alters the form elements as needed. There are some blog post available about writing webform handlers.

Here is how to get the current page from the $form_state.

/** @var \Drupal\webform\WebformSubmissionForm $form_object */
$form_object = $form_state-&gt;getFormObject();
$current_page = $form_state-&gt;get('current_page');