Public API customDomainCreate giving a Problem processing request error

Question

I'm setting up a service with the public API, I'm able to create a domain with serviceDomainCreate, however the customDomainCreate is raising an error. This is for the same service. I can create the custom domain from the UI without any issues.

Here's my GraphQL Query. Any help would be appreciated!
```
{
    'query': 'mutation customDomainCreate($input: CustomDomainCreateInput!) {
        customDomainCreate(input: $input) {
            cnameCheck
            domain
            edgeId
            id
            status
        }
    }', 
    'variables': {
        'input': {
            'environmentId': '...', 
            'serviceId': '...', 
            'projectId': '...', 
            'domain': 'example.com', 
            'targetPort': 80
        }
    }
}
```