FI am not sure but it might be possible that you also have to send the projecrGrantID
Fas it is not on a owned project but rather on a granted project.
FLooking at the api docs this is what you would have to send as well when using the api itself: https://zitadel.com/docs/apis/resources/mgmt/management-service-add-user-grant
Add a user grant for a specific user. User grants are the roles users have for a specific project and organization.
F@adlerhurst @stebenz can you help here?
SWhat I gather from the code it should be 'projectId' and 'projectGrantId', so if you have a granted project please provide both as the definition
SCan you try this combination?