[exim] 4.96-RC1 srs issue

Having an issue with this

remote_forwarded_smtp:
    driver =              smtp
    max_rcpt =            1
    return_path =         ${srs_encode {SRS_SECRET} {$return_path}
{$original_domain}}

error:

remote_forwarded_smtp defer (-1): Failed to expand return path
"${srs_encode {thepassword} {$return_path} {$original_domain}}": empty
address

any ideas how to fix this?