If your tax form states - "Invalid Tax ID number", it may be due to this:
For US-based authors, the IRS is matching the name on line 1 of the W-9 to the tax ID provided (SSN or EIN). The tax name (name on line 1) also has to match the payee name (in payment information provided by the customer/author). The tax ID number (SSN or EIN) provided should be for the tax name. That is what the IRS verifies for us during the TIN match process.
For non-US authors, it is likely because no tax ID number was provided. Your country's equivalent of a Social Security Number or Employer ID Number must be provided. As long as a Foreign TIN is provided, it will be submitted to the IRS for review.