United Travel Bank无法用来订票?

给家人订回国机票,没有选座费用,但是有MUA升舱等待。结账时无法选择United Travel Bank的余额:
Based on your current travel options, travel certificates and United®TravelBank cash are not available. Learn more about travel certificates or TravelBank cash

是因为票不是给本人订的,还是因为有升舱附加费用?考古有人说有选座费的话不能用,但我并没有。参见这里:

丽芬我这个是回国机票啊。之前那个就在回国专区。

这个应该是更加general的问题 跟是否是回国机票没关系 所以我把分区挪过来了

这个gift registry是咋回事?以前没链接过,UTB的钱就不能用了吗?

united.com gift registry
As we keep evolving the digital experience for our travelers, we’ve decided to discontinue the united.com gift registry program. Although you’ll no longer be able to create a new registry or add to your existing one, you can still book travel using the TravelBank balance linked to your current registry until your balance expires.