Why is my potential audience size zero when I am getting Impressions for my ad?




I started running ads for my company yesterday. Initially it didn’t pick up at all so I increased my bid… I have now started seeing Impressions but what is perplexing is that it is still showing Potential Audience Size as Zero. why should that be? Can you think of any reason?
For audience I have uploaded a tailored list of about 5000 Twitter usernames. I know this list has small, but I have run successful campaigns in the past with this list…

What could I be doing wrong this time?