How do I sign up a new client and take payment during a demo call?

Do it live while you have their attention. If you send a link or a sign-up form after the call you may not close them, because business owners are busy and get distracted.

1. Pull up their contact (on the Contacts or Conversations page) and open the Billing tab.
2. Invite them to the system by selecting a plan and clicking Complete purchase. Do not select the plan they are going to buy. Select a separate plan you always invite people to, for example your own package named Starter account.
3. The system emails them that their account is ready, with an Activate account button. Walk them through clicking it, picking a password and logging in.
4. Have them go to Settings, then Billing, and click Upgrade to the plan you want them on, typing their own credit card there. They cannot upgrade to the plan they already have, which is why the invite plan is a different one.
5. Have them open the Usage tab and turn on auto recharge, for example add $20 every time the balance drops below $20, so usage based billing is on as well as the subscription.

When you are starting out, do not enter a client's card yourself with the Add payment method button on their billing page. A new Stripe account has no history with you, and adding many cards from the same IP address looks like fraud, so Stripe's automated systems may flag your account, and it is hard to reach a person if they decide wrongly. There is no set number of cards at which Stripe flags it. Have customers type their own card. Once your Stripe account is established, entering cards for clients is fine.