The OptionRootId for an option can be found in our reference data endpoints. Specifically you need to query the instrument details endpoint GET /ref/v1/instruments. The response will hold a field called RelatedOptionRootsEnhanced which is a list of related options and asset types. For example if we lookup an option on the instrument with UIC=211:
GET https://gateway.saxobank.com/sim/openapi/ref/v1/instruments/details/?Uics=211
The response will hold the following field:
"RelatedOptionRootsEnhanced": [ { "AssetType": "StockOption", "OptionRootId": 309, ... } ],
Where the field OptionRootId is what you are looking for.
More Resources