import { sendTransaction } from "thirdweb";
import { castVoteWithReason } from "thirdweb/extensions/vote";
 
const transaction = castVoteWithReason({
 contract,
 proposalId: ...,
 support: ...,
 reason: ...,
 overrides: {
   ...
 }
});
 
// Send the transaction
await sendTransaction({ transaction, account });