How do I know the business code

[AndreaC1]

It will vary depending on the line of work you are in. If you are not completely sure, just use 999999 which is miscellaneous. This doesn't affect your return at all. See details below for how you can do a search to see if you find one that matches your line of business. 

What is the Business Code used for?

https://ttlc.intuit.com/replies/3300135