If you are entering Column B, and have a zero, you may have an error on your Form 1095-A.
Column B contains information about your "second lowest cost silver plan" (SLCSP) premium.
If column B. in Part III "Coverage Information" has a $0 or is blank for any month someone in your household had coverage from the marketplace, this is likely an error.
If you think this is the case you can use the tax toolfrom Healthcare.gov to determine the premium for your SLCSP. If the number is not correct, it will provide a wrong calculation of your premium tax credit.