For TwoCheckout only. Add additional parameteres to the TwoCheckout checkout URL in the form of an array of arrays of name-value pairs with the format array('name' => 'value').

apply_filters( 'pmpro_twocheckout_return_url_parameters', array() );

Parameters

array

Source

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/classes/gateways/class.pmprogateway_twocheckout.php