The Site Designer is an added bonus for those that don't already have a web presence so that they are able to get up and running online quickly.
If you have your own website you don't have to use the Site Designer in conjunction with Trainerize. You can create a section on your existing website for your online training offers and even have your method of payment for your services on your own site.
For more information on how to link your own website, check out the following help article:
Currently, PayPal is the only payment option that can be used with the Trainerize Site Designer. Other payment options can be used and embedded into more customizable website design systems like those found at Wix, Squarespace, etc.