According to the IRS website, Understanding Your Letter 5591, this letter may be sent when you received the Advanced Premium Tax Credit, for health insurance purchased through the Marketplace, but the IRS either does not have record of you filing a return or they did not receive Form 8962, Premium Tax Credit (PTC), with your return. Form 8962 is used to reconcile any advanced PTC amount with the actual PTC for which you qualify.
When you receive health insurance through the Marketplace, you should receive Form 1095-A. Information from that form is used to complete Form 8962. If you have not filed a return, you should do so as soon as possible. If you did not include Form 8962 with your return, you should complete the form and provide it to the IRS as soon as possible. Instructions to enter Form 1095-A, which will generate Form 8962 are provided below. If the IRS does not receive Form 8962, or receives it late, you may be denied the advanced PTC for 2019.
If you filed a return which included Form 8962, you are instructed to disregard the letter. However, if you receive this letter after your return has been accepted and processed, you may wish to contact the IRS and provide them with the submission ID number (available in the acceptance email you received from TaxAct), and inform them that Form 8962 was included with that filing.
To enter or review Form(s) 1095-A Health Insurance Marketplace Statement:
Access your HealthCare.gov account to review your uploaded Form 1095-A.
To Print Form 8962, Premium Tax Credit (PTC):
Note: If you see a message indicating you have not paid your return fees, click the View/Pay link, which will direct you through the Paper Filing steps. Continue through the screens until you have processed the payment for your product fees and then repeat the steps to print.