Use of variable in external storage not working

🍱 Features & apps files_external_sia
1

Hi All,

I wanted to create folder based on user name in the external storage,as suggested below

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image929×483 42.4 KB

But i couldn’t able to achieve it, am getting the below error, can someone help me here, its been 2 days and i didn’t get any solution…!
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image1412×404 12.3 KB

without $user variable there is no error
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image1410×426 8.69 KB

Please let me know what am missing here

Thanks in advance