I think you will not be able to trade on GDAX because of that address verification problem. Please visit this
LINK to check the full list of several reasons why the identity verification process may fail (lower part of the page).
Quoted the last part which I think related to your case:
We also may not have enough information on record to sufficiently verify your identity at this time. This unfortunately affects our younger customers more often.
There are different requirements in some countries listed in the link above as well.
