A powerful feature is the possibility to show a "Step" after the visitor clicks the submit button of an opt-in form instead of redirecting to a separate "thank you" page.

In order to use this feature, your opt-in form settings should be using the API option, the "HTML Code" option won't work.

Then, in the opt-in form settings, for the option : "WHAT TO DO AFTER SUBMIT" choose "Show Step"

Then a new option will appear, "STEP TO GO TO", choose the "Step" you want to display to your visitor after the opt-in form submit.

Your campaign's steps can be managed/edited via the left control panel.

Showing a 'Step' (Thankyou page) after an opt-in form submit