IRS Form 8821, Tax Information Authorization, allows the individual, corporation, firm, organization, or partnership that you choose to obtain information about your tax account from the IRS, but they cannot act on your behalf.
When a business is sold, both the seller and the buyer are generally required to complete Form 8594, Asset Acquisition Statement Under Section 1060, and attach it to their respective tax returns in the year of transfer. The seller and the buyer each use Form 8594 to allocate the assets among seven asset categories.
Special Allocation Rules For Certain Asset Acquisitions. the gain or loss of the transferor with respect to such acquisition, the consideration received for such assets shall be allocated among such assets acquired in such acquisition in the same manner as amounts are allocated to assets under section 338(b)(5).
Use Form 8883 to report information about transactions involving the deemed sale of corporate assets under section 338. This includes information previously reported on Form 8023, Elections Under Section 338 for Corporations Making Qualified Stock Purchases.
The biggest difference is that an SPA is the sale of all shares, and an APA is the sale of selected assets. Therefore, they are both different transactions and have different procedures.