Thank you for your replies.
I am using Mac OS and IOS on my iPhone. The vault is located on my iCloud. I created a vault on my MacBook and selected the same folder on the iCloud on my mobile. Although my MacBook notes appeared on my phone I realized any new notes did not sync from one device to another.
Then I subscribed to Obsidian Sync and logged into my new account on both devices and then the problem happened.