You have a few options to import relationships
Start here:
https://toolset.com/documentation/user-guides/export-import/how-to-import-content-into-wordpress-using-csv/
As you can see, 2 options jump out immediately for any Post Relationship import because the 3rd does not support this at all natively:
WordPress Ultimate CSV Importer and WP All Import – Toolset Types Add-On plugin
The best option is WordPress Ultimate CSV Importer because it already supports Repeatable Field Groups as well.
Those 2 Plugins developed special approaches to the task and hence follow each a particular workflow.
WordPress Ultimate CSV Importer:
https://toolset.com/documentation/user-guides/export-import/how-to-import-content-into-wordpress-using-csv/import-csv-ultimate-csv-importer-plugin/
Details about Post Relationships:
https://toolset.com/documentation/user-guides/export-import/how-to-import-content-into-wordpress-using-csv/import-csv-ultimate-csv-importer-plugin/how-to-import-posts-from-csv-files-and-maintain-relationships-when-using-the-csv-importer-plugin/
WP All Import – Toolset Types Add-On plugin
https://toolset.com/documentation/user-guides/export-import/how-to-import-content-into-wordpress-using-csv/how-to-import-data-from-a-csv-file-using-the-wp-all-import-toolset-types-add-on-plugin/
Details about Post Relationships:
https://toolset.com/documentation/user-guides/export-import/how-to-import-content-into-wordpress-using-csv/how-to-import-data-from-a-csv-file-using-the-wp-all-import-toolset-types-add-on-plugin/post-relationships/
Both of these documentations are very clear and hold applicable examples. You will, however, need to amend your CSVs to match what those plugins expect.
The documentation also features sample CSV.
Now, https://toolset.com/documentation/user-guides/export-import/importing-content-from-csv-with-post-relationships/ describes the Syntax which Toolset Types expects from a Post in general, in order to trigger an Import opportunity in Toolset → Export/Import.
It describes how to create a CSV with a Column that will be interpreted as a Custom Field by any CSV importer you use.
That column (custom field) should hold for each row (post) the Title or GUI of the related post.
Hence again here we expect a concise structure, and there is no way to "circumnavigate" this. The CSV must be set up exactly like exampled with the data as shown in the DOC.
When such CSV is imported, it will then create posts with that Custom Field and each post will hold as the value in that Custom Field the related posts.
Types now can recognize this and will trigger the import opportunity in Toolset → Export/Import where you can finalize the relationship import.
This is - note - when you do not use any of the previously mentioned 2 plugins which offer specific integration.
Because those, already come with an inbuilt and proprietary method, as you will see on their examples, their CSV are structured differently.
The syntax described in https://toolset.com/documentation/user-guides/export-import/importing-content-from-csv-with-post-relationships/ is onl for plugins that will actually create a Custom Field of that Column, if the import does not do that, it won't work.
This is important.
Most CSV Importers follow that exact structure, so it should not be a problem, but it's important to understand that we are attempting to create a Custom Field here.
The importers generally will expect, that the CSV file will feature a column with heading as the Custom Field Name (key) should be.
In our case that will be _toolset_associations_POST-RELATIONSHIP-SLUG.
You should replace the POST-RELATIONSHIP-SLUG part with the actual slug of your Post relationship.
For example, if you have a relationship "teacher-classes" you would use _toolset_associations_teacher-classes as the column title.
This will then be interpreted as a Custom Field by your CSV importer (most CSV importer works like that)
It will store it in the database for the post which it belongs to in the row.
The importer plugins then generally will expect that for the Custom Field Column just created we add values for each row (post)
In our case, this value must be either the Title or the GUID of the related post.
So, as the value in the column where it intersects with the post row, you will add either the title of the one related post or many titles, of many related posts, as the syntax on the DOC describes.
Possible values and mandatory syntax
1. For one related post:
Parent Post Title
2. For a related post and an intermediary:
{!{Parent Post Title}!} + {!{Intermediary Title}!}
3. For many related posts:
{!{Parent Post Title}!}, {!{Parent Post Title}!}, (etc etc)
What you need to do when populating the CSV is making sure to replace above "Parent Post Title" with the actual title of your "parent" post. But do not remove the {!{}!}, when adding many posts. It's required syntax.
Each row in your CSV will now have a distinct value for the _toolset_associations_POST-RELATIONSHIP-SLUG column. Each value should be formatted like above shown and hold either Parent Post Title or GUID
Now, when you import these Posts with any importer, it creates the posts and adds the Custom Fields as we specified.
This is outlined nicely in this example:
https://toolset.com/documentation/user-guides/export-import/importing-content-from-csv-with-post-relationships/#an-example-of-how-a-csv-would-look-like > These associations exported to CSV file would look like:
That's how your CSV should look like to be ready for the relationship import.
This is valid if you use any Importer unless WP Ultimate CSV Importer Pro or WP All Import – Toolset Types Add-On plugin
I think you will have to amend your CSV according to the above structures
