HTTP page has internal links to HTTPS issue means that HTTP pages linking to HTTPS pages on your website.
The importance of the issue
Search engines make all efforts to ensure website security, so the application of the HTTPS protocol is currently highly preferable, though not required. The application of HTTPS is considered to be a good practice and a criteria of the website’s positive ranking.
When the HTTP protocol is applied, Chrome browser that is preferred by 61% of the Internet users, according to w3counter, sends an insecurity notification able to affect the user’s impression about your website, as well as its conversion and search positioning.
How to check the issue
Using any browser is enough to check the issue. Open the source code of the flawed page. To do this, click the right mouse button at any spot of the page and choose “browse the code” option, or apply an online tool https://codebeautify.org/source-code-viewer
Find the links using the HTTPS protocol in the page’s code.
How to fix this issue
You should strive to switch your entire website to using the https protocol. Follow this migration guideline https://www.searchenginejournal.com/https-migration-guide/195103/