myCRED Transfer Fee example

add_filter( 'mycred_add', 'mycred_apply_transfer_fee', 20, 3 );
function mycred_apply_transfer_fee( $reply, $request, $mycred ) {
    // If another filter declines this transfer ignore this request
    if ( $reply === false ) return $reply;

    // Make sure this is a transfer instance
    if ( $request['ref'] != 'transfer' ) return $reply;

    // In this example, we will deduct 1 point from the transfer
    // So if John transfers 10 points to Sara, we want to make sure
    // Sara only gets 10-1 = 9 points.

    // Make sure this is the transfer instance for Sara getting her points
    // We can diferenciate between John loosing his points and Sara getting hers
    // by making sure the amount is positive as Johns amount would be negative
    if ( $request['amount'] > 0 ) {

        // Deduct the fee. Note! DO NOT use the mycred_add or mycred_subtract functions
        // in this filter or you will create an infinite loop as both functions use this
        // filter. Instead we use the myCRED Settings object to take out the transfer fee.
        $mycred->update_users_balance( $request['user_id'], 0-1 );

        // Now Sara has been charged 1 point. We now need to add a log entry
        $mycred->add_to_log(
            'transfer',
            $request['user_id'],
            0-1,
            'Transfer Fee'
        );

        // Now we just need to tell myCRED to add Sara the original 10 points John sent.
        // Since we have already deducted the "fee" it does not matter that she will receive
        // the full 10 points now.
        return true;
    }

    // Always return a reply or you brake everything!
    return $reply;
}