I completed Form 2210 Part I and checked Part II Box A with a note "85% waiver". However, my federal return was rejected. What should I do?

My 2018 withholding is less than what I owe. However, it is more than 85% of what I owe so I do qualify for the 85% waiver under the "Tax reform waiver" according to the IRS Instructions for Form 2210.

However, my federal return (through TurboTax efile) was rejected on 2/17/19 with a reason that "if If Form 2210, Part II, Line A checkbox 'WaiverOfEntirePenaltyInd' is checked, then [WaiverExplanationStatement] must be attached to Form 2210". In the "What needs to be done" section, it suggests that I have file the return by mail when I am eligible for the 85% waiver.