[Premium]Setting PreWarmed Instance count of azure function app in premium plan using ARM template

I am trying to create an azure function app using deployed under premium plan using ARM template. In the template used I have added the property "preWarmedInstanceCount" under Microsoft.Web/sites/config/web. I am using the latest apiVersion 2018-11-01 for the Microsoft.Web/sites resource. When I deploy the template I am getting the error "siteConfig.PreWarmedInstanceCount is invalid. It is only supported for 2019-03-01 api-version or newer."

To fix the error I tried changing the API version to "2019-03-01" then I started getting the error saying "NoRegisteredProviderFound : No registered resource provider found for location 'westus' and API version '2018-12-01-alpha' for type 'sites'. The supported api-versions are '2018-11-01, 2018-02-01, 2016-08-01, 2015-08-01-preview, 2016-03-01, 2015-08-01, 2015-07-01, 2015-06-01, 2015-05-01, 2015-04-01, 2015-02-01, 2014-11-01, 2014-06-01, 2014-04-01, 2014-04-01-preview, 2015-01-01, 2015-11-01, 2016-09-01, 2017-08-01, 2018-12-01-alpha'. The supported locations are 'centralus, northeurope, westeurope, southeastasia, westus, eastus, japaneast, eastasia, eastus2, northcentralus, southcentralus, brazilsouth, australiaeast, australiasoutheast, southindia, canadacentral, canadaeast, ukwest, uksouth, westus2, msftwestus, msfteastus, msfteastasia, msftnortheurope, eastus2stage, centralusstage, northcentralusstage, francecentral, southafricanorth, japanwest, centralindia, koreacentral, westindia, australiacentral, germanywestcentral, koreasouth, westcentralus, eastasiastage'".

Can someone help me to set the pre warmed instance count using ARM template?