Error on Add Form

I just installed this plugin to tinker and was following the Getting Started guide. The Add Form option shows this error:

Fatal error: Uncaught Error: [] operator not supported for strings in /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/formatting.php:443 Stack trace: #0 /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/libraries/cmb2/includes/CMB2_Base.php(283): give_cmb_amount_field_render_row_cb(Array, Object(CMB2_Field)) #1 /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/libraries/cmb2/includes/CMB2_Base.php(258): CMB2_Base->do_callback('give_cmb_amount...') #2 /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/libraries/cmb2/includes/CMB2_Base.php(235): CMB2_Base->get_param_callback_result('render_row_cb') #3 /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/libraries/cmb2/includes/CMB2_Field.php(759): CMB2_Base->peform_param_callback('render_row_cb') #4 /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/libraries/cmb2/includes/CMB2.php(315): CMB2_Field->render_field in /var/sites/h/hirenandsonal.co.uk/public_html/wp-content/plugins/give/includes/formatting.php on line 443