I hate to be bearer of bad news, but unused invitation rewards do not exist for few months now.
You can always send invites to me in pm (or by registering on idena.site) and when some good candidate comes along, I will hand them out. I ask them for training certificate and give them suggestions on how to setup their pc.
Damn thats a bad news. And not bcause of the fact that I did not get few $$ last epochs. Its because it was in fact a good feature. Someone did not have anyone worth to invite ... he simply did not invite at all. Now he will give it to anyone, random telegram account, most likely bot, that is collecting all invitation available to try going random. I think it will lower average network node quality.