Why am I redirected to Shopify to approve something when changing my Deskhero plan?

For workspaces billed via Shopify, "to change your plan, you'll be redirected to Shopify to approve the new subscription terms". Deskhero also proposes a Monthly Spending Cap in dollars, calculated from your current number of users and pending invites; you can raise this cap so you do not need to re-approve the subscription every time you add a new user.