The file operation program is not updating

def update_server_config(file_path, key, value):
# Read the existing content of the server configuration file
with open(file_path, 'r') as file:
lines = file.readlines()

# Update the configuration value for the specified key
with open(file_path, 'w') as file:
for line in lines:
# Check if the line starts with the specified key
if key in line:
# Update the line with the new value
file.write(key + "=" + value + "\n")
print("File update successfully")
else:
# Keep the existing line as it is
file.write(line)
print("No change done")

# Path to the server configuration file
server_config_file = 'server.conf'

# Key and new value for updating the server configuration
key_to_update = 'PORT'
new_value = '9000' # New maximum connections allowed

# Update the server configuration file
update_server_config(server_config_file, key_to_update, new_value)

This program is running but it is not updating to new value.