let invoice = builder.clone().build_signed(|hash| {
secp_ctx.sign_recoverable(hash, &private_key)
}).unwrap();
assert!(invoice.check_signature().is_ok());
let invoice = builder.clone().build_signed(|hash| {
secp_ctx.sign_recoverable(hash, &private_key)
}).unwrap();
assert!(invoice.check_signature().is_ok());