A broker is nit your friend who refuses to buy junk food for you because he suspects you’ll be sick.

A broker is yiur fiduciary/agent; their discretion at refusing your order should be limited to well defined circumstances, and I would be surprised if this is one of them.

(I would not be surprised if the EULA lets them do what they want, but I would be surprised if it would actually be found legal in court —- though it will likely take ages to test because it likely contains a binding arbitration clause)