Error: ERROR_WRONG_USER_KEY
This error referring to one of the 2 following cases:

You are using wrong API key, so you can double check that you are using the right one.
Navigate to your dashboard, here you can see that you have 15 threads
Which mean you can solve 15 captchas on-time
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Now click on API KEY

Copy your API key, And use in your software!
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Check more about How to Get Started

You may not have any active subscription, in this case this is the error you will see as well.

In this case you need to check if you already have threads in your account;
Navigate to your dashboard, here you can see that you have 15 threads
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If you see it 0, then you have no active orders, in this case you will need to subscribe to a new plan,
Navigate to "home page" Choose your plan and subscribe.
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For more info Check How to Get Started