Thanks for asking question! If you are receiving "App Service Plan Create operation is throttled for subscription" you may want to know that App Service Plans have a 10 per region limit on the Free SKU and 10 per resource group on Shared SKU and further limits according to SKU is listed here.
Depending on your plans you would need to either move to higher plan, or raise a support ticket to see if the limit can be raised you may also want to check the other limits in that link.
In case you don't feel you are hitting any limit then you would need to raise a support case.
Please let me know if further query or issue remains.