Attests that caller was referred by referrer. The event is the
only output: a successful simulation is the pre-flight.
env - Access to the Soroban environment.caller - The referred wallet. Its authorization is required.referrer - The referring wallet.ReferralError::SelfReferral - If caller equals referrer.["attributed", referee: Address, referrer: Address]fn attribute(
env: soroban_sdk::Env,
caller: soroban_sdk::Address,
referrer: soroban_sdk::Address,
)