Manual payments
When you have enabled a payment provider, you can choose to accept ad-hoc payments from members. If you want to take manual card payments from members, you can enable this at Admin > Settings > Payments and enable Allow Ad Hoc Payments.
When enabled, a Make a Payment menu item will be added to the site. When visiting this page, the member will be able to enter a description or reason for the payment and the amount to pay.
They will then be taken to the payment screen to complete the payment. Once the payment has been made, the will receive a payment receipt by email.