You can use the single-player SDK by registering as a developer on the following page.
▼VRoid Hub API / SDK Developer Registration
https://hub.vroid.com/developer/registration
For inquiries about the multiplayer SDK or upload SDK, please contact us using the following form.
▼VRoid SDK inquiry form
https://www.pixiv.net/support?mode=inquiry&type=43&service=vroid-sdk&subject=VRoid