When I send a SOAP request to DocuSign it is showing an error: This Account lacks sufficient permissions. In-Session permission required when specifying a captive recipient.
DocuSign developer sandboxes have this enabled by default so you can test Embedded Signing (and sending, etc) before going live.
In terms of live production accounts- not all accounts have embedding enabled so ensure you have purchased an account that has it. If you are getting this error in production you most likely need to upgrade.