Function deliver 

pub async fn deliver(
    client: &Client,
    inbox: &Url,
    body: &[u8],
    key: &SenderKey,
    first: Scheme,
) -> Result<Scheme, DeliveryError>

Deliver body to inbox, signed with key, trying first and then the other scheme if first is refused. Returns the scheme that was accepted.

Errors

When neither scheme is accepted, or the request fails for another reason.