Coding / SEO edits for a PHP/MySQL/Linux based platform

I have a web-based application built on PHP/MySQL/Linux Platform, it's great but currently it has some SEO related errors and needs a bit of coding done. If you put the url in here https://www.seoptimer.com/www.supremehiring.com you'll see what it needs. I need to do everything, I'm also interested in having the stripe payment gateway integrated with the site. Please look at the site and let me know what you can do before sending a proposal.