Please go to your Merchant dashboard, select the "API keys" area, and click "Activate".

Enter your 2FA code and click "Activate" to activate your API key and see your secret.

You will be able to see your secret after the activation.

Please note that you will not be able to see the "Activate API key" window again after dismissing it. Your secret will be concealed and you will be unable to recover it; thus, please preserve it in a secure location and do not communicate it over messengers or email.