You’re welcome.
In order to get the values from a drop down please review the dropdown API - https://www.wix.com/code/reference/$w.Dropdown.html. Generally speaking, you should search for APIs within the wix API code reference Velo API Reference - Wix.com
Each choice (although you only mentioned size) would be a key in your dictionary so it should be just:
“choices”: { “Size”: “Small” }