Business Pay Online. 1. First, register with the Ohio Secretary of State.Registration information as well as forms are available online(opens in a new window) or at (877) SOS-FILE. If a vendor stops making taxable retail sales, a final UST1 must be filed and all taxes must be paid within 15 days of the final sale. File online- Save paper, save time, start your business online. A purchaser of the assets of a business will be liable for any unpaid sales tax of the seller, as well as any accrued interest and penalties related thereto. Small businesses subject to the tax must register for the CAT through the Ohio Business Gateway, the state's online filing and payment system. Starting a business in Ohio is a relatively streamlined process, but it involves some paperwork to get going. Learn how to set up a business in Ohio. How to Start a Business in Ohio ; Don't Make These Six Common Mistakes in Your Single Member LLC!