post https://api.hel.io/v1/transaction/headless/prepare
Prepares a Solana headless transaction. Returns a payload that the payer can sign and submit.
NOTE: When using Helio on mainnet, set your Base URL to https://api.hel.io and generate your API keys from moonpay.hel.io . For testnet, use https://api.dev.hel.io and generate your API keys from moonpay.dev.hel.io.