Your issue may have been caused by incorrect permissions. Coinbase also did have an outage and also updated their API and UI. You might have made your api call then and it might have failed. I hope this explained any questions you might have had.
So please check all required setting as shown below in your coinbase account:
https://support.coinbase.com/customer/en/portal/articles/1914910-how-can-i-generate-api-keys-for-my-merchant-account-
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