You can find your Merchant ID and Merchant Key in your Payfast account. Here is also a link to the Payfast support page to guide you with this: https://support.payfast.co.za/portal/en/kb/articles/where-is-my-merchant-id-and-key
In the case you cannot see your Merchant ID and Key in your Payfast account, it might be that your Payfast account is not yet activated. The key and ID indeed only become visible once your Payfast account is activated. To inquire about this, you can contact the Payfast support through the page https://www.payfast.co.za/contact so that they can assist you with this. Unfortunately we do not have access to their system, so cannot check that for you, please accept my apologies about this.