We are using DocuSign REST API v2, and we are using the \"Modify User Account Settings\" method
Endpoint: /accounts/{accountId}/users/{userId}/settings
The updating of this setting (canManageAccount) has been broken in REST for awhile now, it works in SOAP though. There is a bug with DocuSign Engineering to address the REST portion, I do not know when it will be fixed and live in Production though.
How to do it in SOAP
SOAP: https://demo.docusign.net/api/3.0/dsapi.asmx
{accountId}
{userId}
true