I got audited by the state of Massachusetts, USA, due to a mistake I did when filing my 2015 Form 1 (mirror). The audit's conclusion was that I have to pay some amount to Massachusetts, which includes some interest (15.124314442%).
After fixing the mistake, it turns out that Massachusetts is actually owing me money (the tax refund as mentioned on line 46 in Form 1 is higher than what I reported when I first filed form 1 in 2016). What interest can I claim on it? Do I use the same interest rate as they used? Or perhaps I am not entitled to any interest since I made the reporting mistake?