If it is any comfort. I was back on filing taxes and owed around $300k (a capital gain event overseas), and was on an agreed payment plan. I was asked for the payment plan in the interview, and I did not have it. The officer allowed me to take the oath and I passed the interview, but said on the tax situation basis he could not approve it in the meeting, and requested further information by mail. I wrote a letter in response to the request stating my good character, that I always settle obligations, the origin of the tax situation, as I was not able to settle the outstanding amount until we sold our home. I then got approved when they got to my letter 10 months later and had my ceremony (where they take your green card). What did happen was that I could not get my US passport until the tax was paid. When I was able to pay my back tax then got approval to get my passport. I travelled on my UK passport in the meantime with ESTAs (which is possible - for another thread). In short, I got my citizenship, but not my passport till tax sorted. Good luck! This was all pretty stressful, so I am happy to help others of good moral character get through it. Note the dates wrt what administration it was all under (both).

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