If you have recently upgraded your Opencart software above version
2.++ then you can may face this problem. Because Opencart added this new
feature for store security purpose in Opencart admin panel.
So I think here is solution for your problem just try to follow given below steps :
Step:1
Login to your Opencart admin panel
www.yourstore/admin
Step:2
Now left admin menu go to System >> Users >> API
Now delete “default API” and create new API and generate new keys according to below picture.
At “IP address” section, it will tell you what ip address are you using now. copy that Ip address and add the address.
Now go to System >> Settings >> Edit Store >> click on “Options” tab >> API users
In API users select your new created API and save settings.
Now you can add IP and next time “incorrect api key” error will not show in Opencart.