Page was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint

I have a blog which it is hosted somewhere else and it is WordPress engine. The web host owner allow us to add some WordPress plugins, WP Statistics is one of them. I installed it and I found wp-statistics is not loading in many pages under Statistics (Overview, Hits, Visitors…etc) in admin page and I can see some error message when open F12 Developer tool. The errors are:

1) admin.php?page=wps_pages_page:1
Mixed Content: The page at ‘https://xxxxx.com/kenlin/wp-admin/admin.php?page=wps_pages_page’ was loaded over HTTPS, but requested an insecure XMLHttpRequest endpoint ‘http://xxxxx.com/kenlin/wp-json/wp-statistics/v2/metabox/?ago=30&name=top-pages-chart&_=1616388533622’. This request has been blocked; the content must be served over HTTPS.

2) VM4598:1
Uncaught SyntaxError: Unexpected token u in JSON at position 0
at JSON.parse (<anonymous>)
at Object.h.error_meta_box_data (admin.min.js?ver=13.0.6:1)
at Object.error (admin.min.js?ver=13.0.6:1)
at c (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,moxiejs,plupload,jquery-ui-tooltip&ver=5.6.2:2)
at Object.fireWith [as rejectWith] (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,moxiejs,plupload,jquery-ui-tooltip&ver=5.6.2:2)
at l (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,moxiejs,plupload,jquery-ui-tooltip&ver=5.6.2:2)
at XMLHttpRequest.<anonymous> (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,moxiejs,plupload,jquery-ui-tooltip&ver=5.6.2:2)

WP-Statistics version: 13.0.6
PhPy: 7.3.13
Wordpress: 5.6.2