Follow below mention steps to generate Merchant ID and Merchant Key:
Step 1 : Login else register on payfast.com
Step 2 :On Dashboard you will get Merchant ID and Merchant Key, Copy and paste it in https://snappy.appypie.com
Step 3 : Choose Settings>>Integration
Step 4 : If you want to accept recurring payments then click on Add Passphase button under
Step 5 : Here you need to enter Passphase
Note:You can enter any alphanumeric('a-z', 'A-Z', '0-9' and ‘.,-_/‘) text