Strange error during API call (RequestError.UNKNOWN @)

Hello Guys,

I'm trying to make a call to Adwords Express API.

I'm using my production developer token and test client account.

When I'm trying to get businesses - error RequestError.UNKNOWN @ occurs.

I have created new Ad on my Express account but error occurs: 

Your ads aren't running because your account balance is exhausted. - Please make a payment. Fix it

Do I need to pay for my ads on test account?

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