1 month ago, I launched a mobile app called Spotiplus that helps Spotify users to design and upload playlist covers images straight to Spotify without the need of the desktop app.
The app was trending on Reddit (/r/spotify) and did well on ProductHunt too,
In last week, I found that Spotify adopted the same feature or 1/2 of the feature by allowing the users to upload custom covers.
I don't know if it's a coincidence or my product proved the need of this feature so that, it incited Spotify to work on it.
(https://newsroom.spotify.com/2020-12-08/how-to-upload-a-custom-playlist-image-using-your-phone/)
That said, this won't stop me from improving the product.
Some stats about the app:
If you'd like to give a try to Spotiplus, visit iOS AppStore or Android Playstore
Doubtful that they copied it within a month. I bet Spotify is big enough now that they aren't very agile in these types of releases and have been planning this for the whole quarter (especially getting a blog post written about it as well).
Great job building something people are enjoying.
You built something people want - that's great! From my perspective, it seems like this would become a Spotify feature eventually and not a stand-alone product. Ideally, that would have happened by them contacting you to buy it, but instead either they developed it independently or were inspired by your product. I'm not sure if there's any reliable way to find out what happened.