Unable to submit the project

I have finished the build a celestial project but whenever I click the 'I ‘ve completed this challenge’ button, it always notifies me that ‘You must complete this project first’.
Is there any solution to this situation?

If you read the top of the screen, it says you have to save your project to a public repository (like github). After creating the repository you can just copy the link and paste it in and the certification will pass.