I’m uploading organizations and people and I have multiline addresses. The secret is to use CHAR(10) if you’re on a PC or CHAR(13) if you are on a Mac to create the line break in the cell. For example
|2||=A2 & CHAR(13) & B2||123 Main Street||Apartment 12|
The API on the other hand encodes those as “\n” since its JSON.
Locations are fun since there’s no way to manage them directly. Definitely no REST endpoint. You create them when you create the organization. If you use the API you can provide the ID of an existing location. But no way I can see to upload a location ID.