firewall.js | js creates an iframe that blocks

I am trying to deploy the below Palo Alto deployment to an Azure environment. We are using it as an internal firewall for the various features it provides that NSGs don't, so we don't want a public IP. We're using a virtual gateway and sticking the firewall behind it in an active-active pair (the load balancer, NSGs, etc. are being done in a separate template).

I've been trying to get this template to work for a while now, but I'm stuck on deploying the two VMs with multiple NICs. I keep getting this error:

ERROR: Azure Error: InvalidTemplate Message: Deployment template validation failed: 'The template variable 'nicName' is not valid: The template function 'copyIndex' is not expected at this location. The function can only be used in a resource with copy specified. Please see https://aka.ms/arm-copy for usage details.. Please see https://aka.ms/arm-template-expressions for usage details.'.

I've tried a bunch of fixes - changing the variable syntax, changing the syntax of the resource, but none of them are working. I've checked the Azure documentation on using the copyIndex feature, but I can't see where I'm going wrong. I was hoping someone with a bit more experience could point out where my syntax is wrong and provide suggestions on how to correct it?

Many thanks, template is below: