An assessment cannot be considered valid if it does not indicate a specific period or due date within which the alleged tax liabilities shall be paid.

An assessment must be sent to and received by a taxpayer, and must demand payment of taxes described therein within a specific period. In other words, assessment is a notice to the effect that the amount therein stated is due as a tax and a demand for the payment thereof. It fixes and determines the tax liability of a taxpayer. In the Audit Result/Assessment Notice in this case, there is no indicia of any due dates. The due dates in the assessment notices were left

blank. Thus, in effect, the FAN does not amount to a formal demand but a mere request for payment. For lack of a definite and unequivocal demand for payment of a certain date and for want of due process, the assessment is void. (Commissioner of Internal Revenue vs. Fitness By Design, Inc. CTA EB No. 970, July 14, 2014)