A taxonomy code is a unique ten character alphanumeric code that enables providers to identify their specialty at the claim level. This is the number you'll see in box 33b of your insurance claims.
If you need help finding your taxonomy code, go to www.npiregistry.cms.hhs.gov and run a search using your NPI so you can find it.
Your SimplePractice account includes the taxonomy code 101YM0800X which is the taxonomy code for a Mental Health Counselor. If that's not your taxonomy code, you can easily update it in your account by going to My Account > Settings > Billing > Insurance.