It is not possible to resolve conflicts of package-lock.json in GitHub's merge tool and you need to do a manual merge.

1. Update the main branch with the latest changes:

   git checkout main
   git pull
   

2. Merge your feature branch into main:

   git merge mybranch
   

   You will see something like the following message:

   Auto-merging package-lock.json
   CONFLICT (content): Merge conflict in package-lock.json
   Auto-merging package.json
   CONFLICT (content): Merge conflict in package.json
   Automatic merge failed; fix conflicts and then commit the result.
   

3. Open your editor (e.g. VSCode) and:
   • Carefully resolve any conflict in package.json.
   • Ignore the conflicts in package-lock.json.
4. Install packages, which will re-generate package-lock.json: npm install
5. "Test drive" your application to make sure the conflicts in package.json have been resolved correctly: npm start
6. If the application is starting (i.e. there are no missing dependencies), add all changes and finish the merge:

   git add --update
   git commit
   

   (Make sure not to commit the *.orig files!)
7. If everything looks fine, push to GitHub:

   git push