How about using Postman?
It helps to verify the response.

I got link data using Postman.
My test steps are below.

1. Get Enterprise Logical ID
I got my enterpse logicalId via API v1.

Request: Post

"https://<vco-fqdn>/portal/rest/enterprise/getEnterprise"

I got enterpriseLogicalId like this.
xxxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

2. Get Edge Logical ID
I got my edge logicalId via API v1.

Request: Post

https://<vco-fqdn>/portal/rest/enterprise/getEnterpriseEdges

I got edgeLogicalId like this.
yyyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyy

3. Get Link stats
Request: Get
https://{vco-fqdn}//api/sdwan/v2/enterprises/{enterpriseLogicalId}/edges/{edgeLogicalId}/linkStats