This is a current and known limitation with our API - tags like order tags and customer tags don’t currently support pagination. You can get the first 250 but you won’t be able to use after to get the next.
The Bulk Operation API can be used to retrieve all resources for a given query and skip pagination.
That might be a solution.
The downside is that it’s not synchronous, but I’m imagining that you’re trying to retrieve all of these tags so you can provide an autocomplete dropdown UI element for your app.
Thanks for the suggestion, but as you probably know this is a once instance operation per shop at any time (which would not work for us), and even the minimum query would take way too long.