@kisuke I fixed my issue. I was using an Indian Roku developer account and a Dynamic keyboard isn't available for an Indian account. It worked for a US account. Make sure you are using a valid geographically compatible account.
Glad it worked for you @rashmikapil2. I am in Brazil, with Portuguese language. In that documentation (https://support.roku.com/en-gb/article/208756908), it says "Voice search and voice control is supported in English, German, Portuguese, and Spanish" but it still didn't work. I'm still waiting for someone from Roku to help us here.