Pushing to BitBucket with an SSH key using gitpython

Question

I'm trying to push some files to BitBucket using gitpython and an SSH key. It works fine when I do it through Git Bash, but when I try it using gitpython I keep getting this error: Cmd('git') failed due to: exit code(128) cmdline: git push --porcelain -- origin stderr: 'fatal: Could not read from remote repository.' Any help appreciated, thanks! Code below:

import git
    def add_and_commit(repo_dir, commit_message):
        try:
            print('Beginning BitBucket Push...') 
            git_ssh_identity_file = r"C:\Users\josh\.ssh\id_ed25519"
            git_ssh_cmd = 'ssh -i %s' % git_ssh_identity_file
            with git.Git().custom_environment(GIT_SSH_COMMAND=git_ssh_cmd):
                repo = git.Repo(repo_dir) 
                # Get a list of all mxliff files in the directory
                all_files = []
                for root, dirs, files in os.walk(repo_dir):
                    for file in files:
                        file_path = os.path.join(root, file)
                        if file.endswith(".mxliff"):
                            all_files.append(file_path)
    
                repo.index.add(all_files)         
    
                origin = repo.remote(name='origin') 
                
    
                existing_branch = repo.heads['main']
                existing_branch.checkout() 
    
                repo.index.commit(commit_message) 
                print('Commited successfully') 
                origin.push() 
                print('Pushed changes to origin')
        except Exception as e:
            print(f'Error when pushing to BitBucket: {e}')
            errors.append(f'Error when pushing to BitBucket: {e}')