Hi Pradeep,
Thanks for reaching out. With regards to your concern about setting category to "Add to cart" or "Begin checkout" using Adwords API, it is not possible via AdWords API. To solve this problem, you can use ConvevsionActionService with conversionaction.category field in the Google Ads API. The Google Ads API is the modern programmatic interface to Google Ads and the next generation of the AdWords API.
For your convenience, you can always check here for service migration between AdWords API and Google Ads API.
Thanks,
Nirmita Patel Google Ads Team