Here are the variables that you can use in Initial Offer Message, Follow-up Message and Goal Achieved Message (whether you use html or not):
:cart_total_currently - total price value of the products in the cart.
:cart_total_goal - value that is set by you in Goal field for cart total, referring to the money amount.
:is_left_to_reach_cart_total_goal - price value that should be added to the client's current purchase in order to reach Goal for cart total and get a reward.
:cart_products_quantity_currently - total quantity of products in cart at the moment when Initial Offer Message or Follow-up Message or Goal Achieved Message is being shown.
:cart_products_quantity_goal - value that is set by you in Goal field for products quantity in cart.
:is_left_to_reach_products_quantity_goal - quantity of products that should be added to the client's current purchase in order to reach Goal for products quantity in cart and get a reward.
:link - link, which name is taken from Link Name field. The http address for the link, which a client is redirected to, is taken from Link URL field.
:button - Button Name field. The http address for the button, where a client is redirected to when clicking the button, is taken from Button URL field.