This can happen when the two branches we're trying to merge have changes on the same line in the same file, or if one branch deleted a file that another branch modified, and so on.
Merge conflict - you have to decide from which branch to keep the change.
After:
git merge dev
Git will notify you about the merge conflict so you can manually remove the changes you don't want to keep, save them, and then:
git add updated_file.md
git commit -m "Merge..."
















