Hi Vincent,
This error can be a result of limited capacity in the region so they restrict which subscriptions are allowed to deploy.
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 West Europe.
1. Navigate to this link to start the process:
https://portal.azure.com/#view/Microsoft_Azure_Support/HelpAndSupportBlade/~/overview
2. Click Create a support request button at top
3. If you see Support AI Assistant as shown below, click Switch to old experience button on right. If not, proceed to step #4
4. Enter quota in the box and click Go
5. Select Others / Service and subscription limits (quotas) and click Next
6. Click Create a support request button, as shown
7. Select Issue type: Service and subscription limits (quotas), Subscription, Quota type: Azure Database for MySQL Flexible Server, click Next
8. Now you should be on Additional details tab. Click Enter details
9. Select Region access or Region access with zonal dependency, select Location you need (West Europe), enter number of cores needed, click Save and continue (below screenshot shows East US, select West Europe instead)
10. 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