Can I add a second business that I own to my QB account?

One QBO account is for one company file. You can use QB Desktop to manage multi company files.

I can help you add another company to your QuickBooks Online account, jared29.

To set up another company, you'll need to create a new QuickBooks Online account because each company file requires a separate subscription.

Also, you can link an additional company to your existing email address by logging in to your current company account while creating a new one, and then click on Add another company.

Here's how to do so:

1. Visit the QuickBooks pricing page and select the subscription option you want for your new company.
2. a. Choose the plan you wish to have.
   b. On the Sign-in page, enter your email address.
   c. Click the Create a new company button. 
   d. Follow the prompts to finish creating the account. 
    

Additionally, refer to this article to learn how to manage multiple company files: Create or add another company file to QuickBooks Online. 

Once the account is created, you can easily switch between companies. Refer to this guide on how do I switch companies for additional information on changing companies seamlessly.  

Let me know if you have any further questions about adding a new company. I am willing to help at any time.

@JustinDaveC  RE: To set up another company, you'll need to create a new QuickBooks Online account because each company file requires a separate subscription.

So, the user has to pay twice, right?

You can create as many QuickBooks files as you want with QuickBooks Desktop at no additional expense, which is just another of the many ways Desktop is better than Online - at least for the customer.