product->options .. refers to the name of the option and not its values.
product->variants->options refers to actual values . beware though product->variants will be deprecated in next release [2024-04]
May be try the following
{
"title": " Title ..... ",
"published": true,
"options": [
"Size"
],
"handle": "handle....",
"variants": [
{
"options": [
"Small"
]
},
{
"options": [
"Large"
]
}
]
}