How come I'm not eligible to youtube custom url?

According to their docs to be eligible you have to have over 100 subscribers which I have, be over a month old which I am and upload channel art which I have. Why is it that they say I am not eligible?
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We also meet all the criteria for a customer URL, but under our channel URL, there is no "Set a custom URL for your channel" link, as per Google's own instructions:
 
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