this is not an error in fact.
It is a warning telling that you are using one version of android support library (26.1.0), and your library is using another version (27.0.2)
To solve this warning you should use version 27.0.2 too. But it might be not required. You may try building the app as it is now.
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solved When i tried to add the library it gives an error of versions .. help me to solve it please [closed]