not have enough resources available to fulfil the request try a different zone

I am having the same issue. I emailed google and figured out this has nothing to do with quota. However, you can try to decrease the need of your instance (eg. decrease RAM, CPUs, GPUs). It might work if you are lucky.

Secondly, if you want to email google again, you will get the message sent from the following template.

Good day! This is XX from Google Cloud Platform Support and I'll be glad to help you from here. First, my apologies that you’re experiencing this issue. Rest assured that the team is working hard to resolve it.

Our goal is to make sure that there are available resources in all zones. This type of issue is rare, when a situation like this occurs or is about to occur, our team is notified immediately and the issue is investigated.

We recommend deploying and balancing your workload across multiple zones or regions to reduce the likelihood of an outage. Please review our documentation [1] which outlines how to build resilient and scalable architectures on Google Cloud Platform.

Again, we want to offer our sincerest apologies. We are working hard to resolve this and make this an exceptionally rare event. I'll be keeping this case open for one (1) business day in case you have additional question related to this matter, otherwise you may disregard this email for this ticket to automatically close.

All the best,

XXXX Google Cloud Platform Support

[1] https://cloud.google.com/solutions/scalable-and-resilient-apps

So, if you ask me how long you are expected to wait and when this issue is likely to happen:

1. I waited for an average of 1.5-3 days.
2. During the weekend (like from Friday to Sunday) daytime EST, GCP has a high probability of unavailable resources.
3. Usually when you have one instance that has this issue, others too. For me, keep trying in different region waste my time. (But, maybe it just that I don't have any luck)

The error message "The zone 'projects/[...]' does not have enough resources available to fulfill the request. Try a different zone, or try again later." is always in reference to a shortage of resources in a zone.

Google recommends spreading your workload across different zones to reduce the impact of these issues on your workload. Otherwise, there isn't much else to do other than wait or try another zone/region

Faced this Issue yesterday [01/Aug/2020] when GCP free credit was over and below steps helped to workaround this.

I was on asia-south-c zone and moved to us zone

Going to my Google Cloud Platform >>> Compute Engine
Went to Snapshots >>> created a snapshot >>> Select your Compute Engine instance
Once snapshot was completed I clicked on my snapshot.
Ended up under "snapshot details". There, on the top, just click create instance. Here you are basically creating an instance with a copy of your disk.
Select your new zone, don't forget to attach GPUs, all previous setting, create new name.
Click create, that's it, your image should now be running in your new zone

No worry of losting configuration as well.