MSP will allow you to take card payments as long as you are on the Pro account. This will require some setup initially.
1. Create an account at Stripe: https://stripe.com/
2. On the dashboard, go to Developers | API Keys
3. In the Restricted API Keys section, Create Restricted Key giving Read / Write access to the Charge option.
4. Open MSP and go to System | Settings | Stripe
5. Copy and paste your Public Key and Restricted Key into the corresponding fields and click Save
6. Go to a Customer or Job | Financial Information | Add Payment
7. Enter an amount to charge as well as a reference then click the credit card button.
8. Enter the credit card information and click Continue.
The card will be charged and assigned to that customer.