which organization you are trying to authenticate? system or tenant one?
if its system , try username@system.-SD [vExpert 14-20, VCIX6-NV&DCV,RHCE,AWS-SAA]
I'm not even sure; I'm just a user of this vCloud instance, and it isn't clear to me what I would use for "organization" or "system". Is there something in the dashboard that indicates what this value would be?