Auto scale on app service not using cli command not working

Below command for auto-scaling on memory usage returning the "UnsupportedMetric"] error

az monitor autoscale rule create --resource-group $COMMON_RESOURCE_GROUP_NAME \
--subscription $ARM_SUBSCRIPTION_ID \
--resource $WEBAPP_NAME \
--resource-type 'Microsoft.Web/sites' \
--autoscale-name "testing" \
--condition "Percentage memory > 70 avg 5m" \
--scale out 1

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#### Document Details

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* ID: 25999d81-221d-052e-03b8-601585f71e3a
* Version Independent ID: ee988a97-bcf4-0ea2-9ab7-cd6af5e98237
* Content: [az monitor autoscale rule](https://docs.microsoft.com/en-us/cli/azure/monitor/autoscale/rule?view=azure-cli-latest)
* Content Source: [src/azure-cli/azure/cli/command_modules/monitor/_help.py](https://github.com/Azure/azure-cli/blob/dev/src/azure-cli/azure/cli/command_modules/monitor/_help.py)
* Service: **monitoring-and-diagnostics**
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**