Your EIN verification letter (sometimes referred to as an EIN confirmation letter, or a Form CP 575) is a document that was mailed to you when you were originally assigned your Employer Identification Number (EIN) by the IRS. It looks like this.
If you're unable to find this letter, call the IRS Business & Specialty Tax Line at 1-800-829-4933 and request a 147c letter to use instead. The hours of operation are 7:00AM - 7:00PM, Monday through Friday. Mainvest cannot request this letter on your behalf.