Is it possible to negate a condition?

I’m trying to build a query that returns all items whose path do NOT contain a string.

I can easily build one that returns items whose path does contain a string:

GET /url?filter[path][CONTAINS]=string

But how can I negate that filter (i.e. ask “return everything the DOES NOT CONTAIN something”)?

You have asked the exact same question at the same date on StackOverflow as well: I have answered it there.

Yes, I did - and your answer was much appreciated! (As a quick summary: I am using Drupal’s JSON:API module, and it does not implement any “does not contain” operator)