The customer is using Octopus Deploy in Azure. The Module AzureRm.ApiManagement is really old from version 2.0.1 (2015).
Latest module Version is 3.8.0.
There was a bug in that module, which we have fixed in 2.2.0, can you upgrade the Modules, so that the customer is unblocked. He is planning to move away from Octopus Deploy in Azure.
We’ll be upgrading the Azure PowerShell modules as part of our release next month.
In the meantime, the customer can always install their own version of Azure PS modules on their server and tell Octopus to use the version installed on the server (and not the version that gets bundled with Octopus). This documentation shows the variable they need to set (eg. Octopus.Action.Azure.UseBundledAzurePowerShellModules set to false).