To purchase a paid subscription for a CrossClave account, navigate to https://billing.crossclave.com/ and log in. Once you've logged in navigate to your subscriptions where you will be shown to have none. Select 'Browse Products' to be redirected to a page where you can select the pro plan.
Once the page opens and you've selected the pro plan to purchase you will need to choose the number of pro plan(s) you would like. If you are simply purchasing for yourself leave the selection at '1' and choose whether you wish to be billed annually or monthly. After deciding select 'Purchase Now'.
At the checkout page enter billing information and your credit card information if paying by card, or the appropriate ACH payment information if purchasing via that method and choose 'Purchase License'. Your order will complete and your account will then be automatically moved to the paid tier.