If you don't get an LED light of any sort when you press that button, then the battery is either completely dead.... which I find it hard to believe for the little energy a LED requires. Or something is disconnected or broken.
Which Junction box are you using, the SM-EW90A or the EW-RS910? Either way, I'd bet on the wires not being fully seated. I'll be happy to be wrong. It matters not to me. Just get it fixed.
Even with long wait times at the bike shops, If I go to the bike shops around me with my bike, they'll come out and give it a once over if I tell them of an issue. If it's going to be something that takes only a moment, they'll fix it then and there, if it will take two moments and some more investigation, they'll ask to keep it and then I go in the rotation of already scheduled bikes.
If you are using some big LBS, you might have trouble doing this successfully.