Box Sign - BadRequest (roles are not working) - .NET

Hello,

I have a problem with the BoxSignRequestSignerCreate object. It works only if I don't provide a Role parameter (default null). When I'm trying to use either BoxSignRequestSignerRole.signer or BoxSignRequestSignerRole.approver it doesn't work. What could be the reason for that behavior?

Code:

var signers = new List<BoxSignRequestSignerCreate>
                {
                    new BoxSignRequestSignerCreate()
                    {
                        Email = "xxxxxxxxxxxx",
                        Role = BoxSignRequestSignerRole.signer,
                    },
                    new BoxSignRequestSignerCreate()
                    {
                        Email = "yyyyyyyyyyy",
                        Role = BoxSignRequestSignerRole.approver,
                    },
                };

Error:

Box.V2.Exceptions.BoxAPIException: 'The API returned an error [BadRequest | 0ca9be4cc604db7b49c8d1333955f9761.0ca9be4cc604db7b49c8d1333955f9761] bad_request - Bad request'

Thanks