How to send partial response fields to external system instead of complete response payload?

Hello all,

I am new to Qualtrics and was looking on Survey - Survey Flow - Webservice option and had a few clarifications on this topic.
So ideally I understand that this webservice element will be triggered only on accessing the survey link based on the placement of the webservice element in the survey flow. i.e. Survey first - Webservice call second.

My scenario is vice versa of above one, where Webservice call is first and then later call the survey. To achieve this I have an external system that calls JSON Event on the Actions tab of survey to create a contact and create distribution and individual survey links to access survey using Qualtrics API.

I am able to achieve this partially, but facing issue on how to send few response fields to external system API instead of sending the complete Qualtrics API response payload from Actions tab as I don't want to call the survey until the responses data is passed to external system.

We have the option to fire and forget from survey flow - webservice where we can limit on the response fields and can use them as embedded data. Is my understanding correct here?
Anything similar to this that can be of achieved from Actions tab with webservice API calls
Any suggestions/guidance here will be really helpful to start with.
Thanks!