mount GCPs buckets with write access
The problem you are having might be because of three things:
-Permissions on the OS after mounting, to solve this mount your bucket with the following command:
sudo mount -t gcsfuse -o implicit_dirs,allow_other,uid=1000,gid=1000 <BUCKET> <PATH>
-Permissions of your service account, to validate this you can go on the consolen to IAM & admin and verify that the service account your VM is using has Storage Admin Role.
-Cloud API Access Scopes: verify under the VM configuration that it has read write or full access for storage.