Why I cant push my new project and getting error: failed to push some refs to ..........etc error

[Chethan V]

Hi I am new to source tree and trying to push my game to bitbucket using source tree. I created a local repository and connected that with my remote repository. But when I try to push it , I am getting the following errors:

git -c diff.mnemonicprefix=false -c core.quotepath=false --no-optional-locks push -v --tags --set-upstream origin master:master
Pushing to https://bitbucket.org/chethanv_7/flappy-universe-7.git
Uploading LFS objects: 100% (300/300), 19 MB | 356 KB/s, done.
To https://bitbucket.org/chethanv_7/flappy-universe-7.git
! [rejected] master -> master (fetch first)
error: failed to push some refs to 'https://bitbucket.org/chethanv_7/flappy-universe-7.git'

hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

You can find the screenshot of the error. How can I overcome this 

[Craig Nodwell]

Hi @Chethan V welcome to the community.
Your local repo and remote repo are out of sync.
There are changes in the remote repo that are not in your local.
You must get those remote changes into your local repo prior to pushing.
Do a pull on the remote repo then redo your push.

[Chethan V]

I tried to pull but got the following error @Craig Nodwell