post https://api.hel.io/v1/auth/external/sign-up
Create a new Helio merchant account using an external authentication method.
NOTE: When using Helio on mainnet, set your Base URL to https://api.hel.io and generate your API keys from app.hel.io . For testnet, use https://api.dev.hel.io and generate your API keys from app.dev.hel.io.