The number of custom tracking domains you can add depends on your subscription plan. Currently it’s:

• • Solo: up to 3 custom domains
• • Team: up to 50 custom domains
• • Enterprise: up to 100 custom domains

If you need more domains on any plan, you can purchase an additional 50-domain add-on by clicking on your email address → Subscription → scrolling to the Add-ons section → clicking “Subscribe”, and completing the billing details to finish your purchase.