Maintaining LTI connection when reloading tool

Community Explorer

Hello, I am the Canvas LMS Manager for my school district and I know PHP and MySQL but have just started dabbling in building LTI tools. I recently forked the Basic LTI Tutorial Using PHP 
and was pretty excited to get some basic tools to embed into Canvas and be able to use the Users information. They were fairly rudimentary tools. Currently, I started writing a slightly more involved tool and have run into a problem that is probably an easy fix for someone who knows what they are doing. (not me!) The tool is still just a one page PHP page but it submits a form back to itself and enters some data into a database and then reloads the page to show the changes. Upon reload of the page however it will drop down to the "This was not a valid LTI launch". I'm assuming I need to store something in a session or something? Basically, if I have an entire tool with several PHP pages how do I maintain the connection? I've been googling the last three days on this and have tried a million things but now am just willing to acknowledge my stupidity with this and reach out and see if anyone can get me a little farther down the road. Thanks.