Hello , How are you?
I just saw your project description carefully.
I am very interested in your project.
I have rich experience in PHP version upgrading.
https://www.freelancer.cn/projects/php/php-php-upgrade/
https://www.freelancer.com/projects/php/Upgrade-php-app-from/
https://www.freelancer.com/projects/mysql/Convert-mysql-mysqli-small-website/
https://www.freelancer.com/projects/php/Get-Website-Built-14697043/
Perhaps , it will be mysql issue.
so , you need to update mysql to mysqli in your php script.
Because Php 5.4 is based on mysql but php5.6~php7.0 is based on mysqli.
I am ready to start your project immediately.
I am sure I can satisfy you surely and complete in a short time.
Please send your message so that we can discuss about your project.