Using an outside class scheduling/payment service within a squarespace template?

Someone asked me to set up a squarespace website for their business in which they teach American Heart Assoc (AHA) and other health training classes (CPR, BLS, etc.). They would like to use a  specific service called Enrollware for the scheduling and payment of these courses because it integrates directly with AHA. My question is whether this can be included in a link or button in a squarespace template or can you only use the class scheduling and payment options that are offered through SS.?

As an update, Enrollware said a potential client can access their scheduling service by clicking on "website name".enrollware.com.   So I guess my question is... can this link be incorporated into a squarespace template, in for example, a button?