Illegal string offset laravel 5

Below is my query which fetches name of user

$userName4 = User::where('_id', '=', $userId4)->first()->name;

Output

CHANDRA PRAKASH SHARMA

Then

$data[$flevel][$userName2[0]['name']][$userName3[0]['name']][$userName4] = $eachSetData4[$level[2]];
// $data[South][Sajeev MT][Jayasheela G][CHANDRA PRAKASH SHARMA] = '1213we23121ws';

But I am getting following error,

Illegal string offset 'CHANDRA PRAKASH SHARMA'

Please help me to resolve this issue.

via Chebli Mohamed