The settings to update your payment methods are available under
Manage --> Advanced Settings --> Site settings --> Payment.
There, you can edit the "Payment method" and click on the "Add payment method" button on the top of the page. Then simply choose the provider you would like to enable.
Campaignion supports Paypal, Payone, Paymill, Stripe, Braintree, SagePay and Manual Direct Debit (for UK or for the SEPA zone). If you don't find any provider to enable, ask More Onion support to install the according feature.
For each payment method, you can add a specific title (the one you'll see in the admin interface) and a generic one (which your supporters and donors will see).
Then, you will have to enter your API keys, i.e. the keys for Campaignion to identify your Paypal, Stripe,... account. In case of doubt, please enter in contact with the support of the corresponding payment method. Also, at least for Stripe and Paymill, be sure to match the keys in the "Personal data mapping" table with the form keys of your actions. For some payment methods, other steps must be done outside Campaignion, as for example whitelisting the Campaignion server. Be sure to follow the description from each individual payment provider on top on the Campaignion configuration!
When this process is completed, all available payment options will show up in the payment select field of the donation form builder. This field is available per default on the list of fields that can be added in your donation form. When editing this field you can pick the tab "Options" and individually enable or disable each payment method that is configured.
Should you have any open question, please contact our support team!