You can find an example of how the middleware.ts file should look like at the end of this page.
  1. You can create a new Upstash account here.
  2. Create a Redis database.
  3. In the details section of the dashboard, get the UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN.
  4. Let’s now update the following variables inside the .env.local in the codebase: 
UPSTASH_REDIS_REST_URL=
UPSTASH_REDIS_REST_TOKEN=
In the codebase, run the following command to install the @upstash/ratelimit package: 
npm install @upstash/redis @upstash/ratelimit
In the middleware.ts file, add an RATE_LIMITED_URLS arr outside of the middleware function. This arr contains the URLs that will be rate limited. 
const RATE_LIMITED_URLS = ["/api/example-call"];
Then, initialise the redis client with the .env variables we just copied: 
const redis = new Redis({
    url: process.env.NEXT_PUBLIC_UPSTASH_REDIS_REST_URL,
    token: process.env.NEXT_PUBLIC_UPSTASH_REDIS_REST_TOKEN,
});
You can now add the rateLimit outside of the middleware function. In our case, we’ll be limiting it to 5 API calls per minute (60 seconds). If a user makes more than 5 API calls in a minute, a 429 response will be returned. 
const ratelimit = new Ratelimit({
    redis: redis,
    limiter: Ratelimit.slidingWindow(5, "60 s"),
});
You’ll just have to add this if statement to check if the URL is rate limited and return the appropriate response and then we’re done. 
if (RATE_LIMITED_URLS.some((url) => request.nextUrl.pathname.startsWith(url))) {
    const ip = request.ip ?? "127.0.0.1";
    const { success } = await ratelimit.limit(ip);

    if (!success) {
        return new NextResponse("Too Many Requests", { status: 429 });
    }
}
Please add this if statement inside the middleware function BUT before the supabaseClient.auth.getUser() function. Otherwise, the rate limit will not work as it will be executed after all the API calls have been made.
Here’s an example of how the middleware.ts file should look like: 
import { Redis } from "@upstash/redis";
import { Ratelimit } from "@upstash/ratelimit";

const RATE_LIMITED_URLS = ["/api/example-call"];

...

const redis = new Redis({
url: process.env.NEXT_PUBLIC_UPSTASH_REDIS_REST_URL,
token: process.env.NEXT_PUBLIC_UPSTASH_REDIS_REST_TOKEN,
});

const ratelimit = new Ratelimit({
redis: redis,
limiter: Ratelimit.slidingWindow(5, "60 s"),
});

export const middleware = async (request: Request) => {
    ...

    if (RATE_LIMITED_URLS.some((url) => request.nextUrl.pathname.startsWith(url))) {
        const ip = request.ip ?? "127.0.0.1";
        const { success } = await ratelimit.limit(ip);

        if (!success) {
            return new NextResponse("Too Many Requests", { status: 429 });
        }
    }

    const supabaseClient = createServerClient(
            process.env.NEXT_PUBLIC_SUPABASE_URL!,
            process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
            {
                cookies: {...},
            },
        );

    ...

};