I think the trick to that, and I could be miss-remembering, was to do it during a quest (maybe it was the tutorial?) hand. I think the first few you are guaranteed to win.

Note that I'm remembering this too from years and years ago, so I could be 100% wrong.

On the main app page is a green and white Lemmy (top left). Tap that. There is a link in the context menu called "remove ads" with a thumbs up emoji.

You need to be on version 25 or newer for the option to appear.

On the main app page is a green and white Lemmy (top left). Tap that. There is a link in the context menu called "remove ads" with a thumbs up emoji.

[EDIT]

You need to be on version 25 or newer for the option to appear.