Automating a survey and reminders

Hi! 

I am currently working on a project where I need to send a survey when an opportunity is closed, followed by reminder surveys at 5 and 10 days if the survey is not completed. In order to send these reminders, I need to use information from the opportunity that identifies the contacts in the approval chain. 

We do not have the paid feedback management tool. 

I created a flow to send the initial survey and that works well and relates the survey invitation to the correct opportunity. My problem is when creating a scheduled flow to check to see if the survey invitation status is not started. I need to be able to relate the survey invitation to the opportunity that it is related to. I created a flow to run when the survey subject object is created to update a custom field on the survey invitation record with the value of the subject id but this is not working. Please let me know what I have wrong here.