SSL page.

Your plugin contain url with http. If it’s installing in a page with ssl the page isn’t green bar.
Problems:
/plugins/acumbamail-signup-forms/assets/alt-checkbox/jquery.alt-checkbox.icon-font.css:12:@import url(https://weloveiconfonts.com/api/?family=fontawesome);

/plugins/acumbamail-signup-forms/inc/frontend.php:74: echo ‘<form id=”wordpress-form-acm” action=”https://acumbamail.com/signup/&#8217;.$chosen_list.’/” method=”POST”>’;

./plugins/acumbamail-signup-forms/inc/frontend.php:105: echo ‘<section class=”subscribe block”><div class=”subscribe-pitch”><h3>’.$title.'</h3><p id=”acumba_info”>’.$subtitle.'<p></div><form id=”wordpress-form-acm” action=”https://acumbamail.com/signup/&#8217;.$chosen_list.’/” method=”POST” class=”subscribe-form”>’;

Solutions:
/plugins/acumbamail-signup-forms/assets/alt-checkbox/jquery.alt-checkbox.icon-font.css:12:@import url(//maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css);

/plugins/acumbamail-signup-forms/inc/frontend.php:74: echo ‘<form id=”wordpress-form-acm” action=”https://acumbamail.com/signup/&#8217;.$chosen_list.’/” method=”POST”>’;

./plugins/acumbamail-signup-forms/inc/frontend.php:105: echo ‘<section class=”subscribe block”><div class=”subscribe-pitch”><h3>’.$title.'</h3><p id=”acumba_info”>’.$subtitle.'<p></div><form id=”wordpress-form-acm” action=”https://acumbamail.com/signup/&#8217;.$chosen_list.’/” method=”POST” class=”subscribe-form”>’;