Adyen Payment

1. Open app/code/community/Adyen/Payment/etc/config.xml and find the following lines:

   <controller_action_predispatch_checkout>
       <observers>
           <adyen_payment_hpp>
               <class>adyen/observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_hpp>
           <adyen_payment_billing_agreement>
               <class>adyen/billing_agreement_observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_billing_agreement>
       </observers>
   </controller_action_predispatch_checkout>
   

   Replace them with:

   <controller_action_predispatch_checkout>
       <observers>
           <adyen_payment_hpp>
               <class>adyen/observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_hpp>
           <adyen_payment_billing_agreement>
               <class>adyen/billing_agreement_observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_billing_agreement>
       </observers>
   </controller_action_predispatch_checkout>
   <controller_action_predispatch_firecheckout>
       <observers>
           <adyen_payment_hpp>
               <class>adyen/observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_hpp>
           <adyen_payment_billing_agreement>
               <class>adyen/billing_agreement_observer</class>
               <method>addMethodsToConfig</method>
           </adyen_payment_billing_agreement>
       </observers>
   </controller_action_predispatch_firecheckout>
   

2. Save the file and clear Magento cache.