What API_KEY and SECRET are used to get Detail on sub-account FUTURES?

I cannot find unambiguous instructions for the API_KEY and Secret required when getting details for sub-account FUTURES.
In addition, I find two different routes in various documents:
in (https://developers.binance.com/docs/sub_account/asset-management/Get-Detail-on-Sub-accounts-Futures-Account-V2) the route is /sapi/v2/sub-account/futures/account NOTE v2 and a futuresType parameter is required.

in https://binance-docs.github.io/apidocs/spot/en/#get-detail-on-sub-account-39-s-futures-account-for-master-accountthe route is /sapi/v1/sub-account/futures/account NOTE v1 and the futuresType parameter is not used.

The master account is a corporate account.

FUTURES is enabled in sub account (there are no funds yet)
I have actually tried both routes (changing parameters accordingly) and get the Signature for this request is not valid error. I am using Java, and all other signature requests work (using master account API_KEY and SECRET). I have also tried from Postman (the collection used the v1 route) and got the same error.
I would appreciate any guidance

For anyone who questions which route to use, after some fiddling around with the Postman collection and environments, I have confirmed that /sapi/v1/sub-account/futures/account is the correct route for a corporate account.
The issue I am now dealing with is that the @ in the email address is being encoded somewhere in the OKHttp/Retrofit2 library (v2.9.0) as %40 rather than the actual @ character, and the signature is then not correct. Postman seems to use the email string as-is and encodes the entire route correctly, so the Postman request now succeeds.
If anyone has experienced this with OKHttp, please respond.

For anyone else using Retrofit2 libraries, the solution turns out to be straightforward once you slog through the solutions to related problems. In short, for Query parameter values that contain characters considered “separators” by Retrofit2 (such as @), the optional Query encoded flag must be set:
(@Query(value = "email", encoded = true) String email, ... other Query parameters...)