Cannot add a class to metabox

You didn’t mention the library you’re using to generate this meta, but i guess it’s the cmb2 library, if it’s so then you should change your array params as follow :

array( 
    'label' => esc_html__( 'Property Lot Size', 'zoacres' ),
    'desc'  => esc_html__( 'Enter lot size of property by number. Do not use any special characters like comma, dot etc... Example 10000', 'zoacres' ), 
    'id'    => $prefix.'lot_size',
    'tab'   => esc_html__( 'Property Details', 'zoacres' ),
    'type'  => 'text',
    'default'   => '',
    'attributes' => array(
       'class' => 'zoacres-main'
     )
),