There is currently an unofficial Square WHMCS module that isn't very good and I won't use it because of this.
Square is a great platform and having a WHMCS payment module would be popular. Currently WHMCS has over 40,000 users according to their website and I know many of these request a Square module (according to their forums).
Please, please, please work with WHMCS to develop an official Square WHMCS Payment Module
