You could always connect by finding the URL being passed in the Power BI service and use that as a Web data source from Power BI desktop. That way you'd be able to create your data model.
There are additional details here which guide you through the insightly portal.
https://docs.microsoft.com/en-us/power-bi/service-connect-to-insightly
There is a section within the above named "Finding Parameters" here it goes through how you can access the insightly portal. Additionally there is information around how to access the insightly API. Please note there is daily limit on the number of calls to this API.
select User Settings from the Insightly profile menu and scroll down.
This string of characters will be used to connect your data to Power BI.
Insightly API documentation can be found here:
https://api.insight.ly/v2.2/Help#!/Overview/Introduction#ratelimit
An example of an API call using the Power BI Web data source is as follows:
https://api.insight.ly/v2.2/Contacts
Using the key which can be found under the "Finding Parameters" tab you're able to populate the below: