I had the same thing happen yesterday. I'm not sure WHY it's happening, but I manually changed it from the app on my phone. I cannot yet figure out how to do it on the computer. (It's is strange than some things can be done only on the app and other things can be done only on the computer . . .)

On your phone, open the request. In the top right-hand corner, click on "modify". Scroll down to the second pet and click on "rate type" Adjust the rate as needed. (You can also adjust the price from the "cost adjustment" button at the bottom.)