Website was built with pure HTML, PHP. and run on Nginx, php7.2-fpm.
Some php need to echo immediately for avoiding long-time response.
Current issue is on iPhone's chrome browser.
Ob_flush()
flush()
This intructions are not working on iPhone's chrome browser after hosting. In local testing, these instructions are working properly.
The developer will fix this issue , and must have experience for this kind of issues.