Hi,
Thanks for posting your concern.
If you want to achieve the same functionality of the Keyword Planner using the AdWords API, then, you would need to use the TargetingIdeaService to do so. You may refer to this documentation to read more about generating targeting ideas and how to implement it.
Also, the link that you provided is the form that you need to complete to request basic access for your developer token. This is required if you wish to use the above service for your production Google Ads account.
Let me know if you have further questions.
Regards,
Ejay
Google Ads API Team