How do I search for a substring using the Confluence search API?

I would like to enter an ID like 6eb1d47ad2b5b4b375c60fae and find results like in Confluence using the API.

However, no matter how I try to set up the CQL, it misses any results that are not 6eb1d47ad2b5b4b375c60fae by itself. However, the UI search bar finds these results (no CQL, just plain text query).

So how do I make the API return the same thing as the UI for a search?

A similar question was asked a year ago here (no response yet): Is /gateway/api/xpsearch-aggregator/search/v2/adva...

Update: I haven’t been able to find a way to fix this in the application I’m building. I ended up adding Google Drive/Docs as an alternative option for wiki writing & documentation since its search API does find results like this. If I do find a way of making it work the same way with Confluence, I will post back here.

I’m trying to learn Atlassian products through questions here… and strangely, when I google this term:
Confluence "xpsearch-aggregator"

Your thread here and the thread you linked are all I can find. A total of two pages of results in Google, no official Atlassian documentation about the API at all.