A question is, why are they already distributing this app without a contract in place and compensation to you? Aside from that, I think the fact that they are selling the app is important and makes the license fee more valuable than a “non-broadcast not for sale” license. Also, this is not a one song deal. Twelve tracks is decent amount of content. You also need to consider if these are existing tracks or were they custom created for the app. Custom writing is also more valuable.
One way to approach this is basing it on what it would cost them if they used a company like pond5. I’ve had “Premium License” sales of $140 (before the split). So $1,680 wouldn’t be out of the question. Of course you saved them hours of work, they didn’t have to search through thousands of tracks to find what they need.
It’s tricky to price now, with music so devalued, subscription sites and etc. Good luck!