Issue in my first app

After doing step 2 :call-a-jira-api from atlassian developer guide ,i want to see my first application in Jira but this error show up. can anyone help me to solve this error!!!
thank you

Can you share the contents of your index.jsx file?

The error indicates that you are trying to call .length on line 13 in a way that is unexpected.

Welcome to the Atlassian Developer Community, @mariemdridi !

Based on your screenshot, you are accessing the app in the project page; to get the issue key in the sample app, you should get it from an issue page/panel. What module did you use for the app - it seems like you used jira:projectPage instead of jira:issuePanel which explains why you aren’t getting the comments properly.