Step 1 - Endpoint
IP address lookups will be under the nearest flights endpoint of the Geo API.
For the first step of changing over to v3 you will need to change the URL to the nearest flight geo endpoint.
https://partners.api.skyscanner.net/apiservices/autosuggest/v1.0/ to https://partners.api.skyscanner.net/apiservices/v3/geo/hierarchy/flights/nearest.
Collection in postman
You can see examples of the new endpoints with this postman collection: