Youtube API Playlists not returning the Playlist

I am using the Playlists endpoint of Youtube's API to get the playlists from a specific channel but it doesn't work for the following channels:

https://www.youtube.com/channel/UCX5fyLRcU05DMa2OVu-qFEQ

https://www.youtube.com/channel/UCwm2mdiUXApmL5bCxHtgJIA

The query I am using:

https://www.googleapis.com/youtube/v3/playlists?channelId=UCwm2mdiUXApmL5bCxHtgJIA&part=snippet&order=date&maxResults=50&key=YOUR_API_KEYhttps://www.googleapis.com/youtube/v3/playlists?channelId=UCX5fyLRcU05DMa2OVu-qFEQ&part=snippet&order=date&maxResults=50&key=YOUR_API_KEY

It doesn't return the videos when I try to target the playlists in these channels using the specif Playlist ID as well. I can see that these channels, playlists and videos are public and searchable.

Is there any reason why the API shouldn't return this playlist that I am missing?

Thank you for your help.

Bartu