unable to create bucket, probing for enable billing option "You can use Cloud Storage after you enable billing". When tried to use "My Trail Billing account" (which was mapped in earlier session with Admin console account to user account) – popped up with
Unable to enable billing
You have reached the limit of projects on which you can enable billing. You can request an increase in your billing quota if you need to enable billing on additional projects.
During the trial period, you have somewhat a quota of "Billing Account Linking Quota", i.e. you can only link a certain number of projects to your Billing Account. The quota can be 3 or 5 or maybe something else (in my case it’s 5).
If you suddenly cannot enable Billing on any new project, it’s likely that you’ve exceeded this so-called quota. You may want to unlink some existing/unused project so that new projects can be linked.