35 ILCS 630/7
When a taxpayer does not pay the tax imposed by this Article to a retailer, such taxpayer shall file a return with the Department and pay the tax upon that portion of gross charges so paid to the retailer during the preceding calendar month by the 15th day of the month following that month. Such return shall be filed on a form prescribed by the Department and shall contain such information as the Department may reasonably require.
When a taxpayer pays a tax imposed by this Article directly to the Department, the Department (upon request therefor from such taxpayer) shall issue an appropriate receipt to such taxpayer showing that he has paid such tax to the Department. Such receipt shall be sufficient to relieve the taxpayer from further liability for the amount of tax to which such receipt may refer.
35 ILCS 630/7