Hi,
When there is limited capacity in the region they restrict which subscriptions are allowed to deploy MySQL Flexible Server. The error will usually be similar to below:
ProvisionNotSupportedForRegion Provisioning in requested region is not supported. Your subscription might not have access to create a server in the selected region.
You should be able to deploy to a different region (e.g. West US 3) or follow instructions below to request access to your preferred region.
Please carefully follow my instructions below to create a new Service and subscription limits (quotas) request to allow access to deploy Azure Database for MySQL Flexible Server in your preferred region.
1. Navigate to this link to start the process:
https://portal.azure.com/#create/Microsoft.Support
2. Enter quota in the box and click Go

3. Select Others / Service and subscription limits (quotas) and click Next

4. Click Create a support request button, as shown

5. Select Issue type: Service and subscription limits (quotas), Subscription, Quota type: Azure Database for MySQL Flexible Server, click Next

6. Now you should be on Additional details tab. Click Enter details

7. Select Region access or Region access with zonal dependency, select Location you need, enter number of cores needed, click Save and continue

8. Finish filling out Additional details tab, click Next, review and click Create. You should receive an automated email within a few minutes.
NOTE: It is possible that they will deny your request due to capacity limit or other reason, but at least you tried.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP