Is the option to tip not very obvious?

I've been sitting with Rover for 4 years. I've sat for tons of dogs over the years, and have had tons of repeat clients. Now, I don't expect a tip at all, but until 2 weeks ago I didn't even know Rover had implemented tipping. A client told me they were looking for someone knew when I met them because their last sitter said they required a "minimum 20% tip", which I found unbelievably tacky of them.

When this owner returned, she said the place that usually allows tipping wasn't there. I was telling her it wasn't necessary (she was super nice and it was an easy job), but she was insistent and ended up PayPal-ing me. I had a 3-day job the very next day and I ended up receiving a tip from them with the review, which blew me away because again, I had never heard of tipping with Rover.

How long has it been around? Does it appear/disappear at random? I find it odd someone with experience with tipping on Rover said it wasn't there one time. Again, I don't expect tips at all, but it started making me feel retroactively self-conscious that no one in however long it's been around had felt I did well enough to tip, unless of course it's not showing up for them either.