diff --git a/keyserver/src/keyserver.js b/keyserver/src/keyserver.js
index 3eb367f1d..38c3403c7 100644
--- a/keyserver/src/keyserver.js
+++ b/keyserver/src/keyserver.js
@@ -1,199 +1,206 @@
 // @flow
 
 import olm from '@matrix-org/olm';
 import cluster from 'cluster';
 import cookieParser from 'cookie-parser';
 import { detect as detectBrowser } from 'detect-browser';
 import express from 'express';
 import expressWs from 'express-ws';
 import os from 'os';
 
 import stores from 'lib/facts/stores.js';
 
 import './cron/cron.js';
 import { migrate } from './database/migrations.js';
 import { jsonEndpoints } from './endpoints.js';
 import { emailSubscriptionResponder } from './responders/comm-landing-responders.js';
 import {
   jsonHandler,
   httpGetHandler,
   downloadHandler,
   htmlHandler,
   uploadHandler,
 } from './responders/handlers.js';
 import landingHandler from './responders/landing-handler.js';
 import { errorReportDownloadResponder } from './responders/report-responders.js';
 import {
   createNewVersionResponder,
   markVersionDeployedResponder,
 } from './responders/version-responders.js';
 import { websiteResponder } from './responders/website-responders.js';
 import { webWorkerResponder } from './responders/webworker-responders.js';
 import { onConnection } from './socket/socket.js';
 import {
   multerProcessor,
   multimediaUploadResponder,
   uploadDownloadResponder,
 } from './uploads/uploads.js';
 import {
   prefetchAllURLFacts,
   getSquadCalURLFacts,
   getLandingURLFacts,
   getCommAppURLFacts,
 } from './utils/urls.js';
 
+const inviteSecretRegex = /^[a-z0-9]+$/i;
+
 (async () => {
   await olm.init();
   await prefetchAllURLFacts();
 
   const squadCalBaseRoutePath = getSquadCalURLFacts()?.baseRoutePath;
   const landingBaseRoutePath = getLandingURLFacts()?.baseRoutePath;
   const commAppBaseRoutePath = getCommAppURLFacts()?.baseRoutePath;
 
   const compiledFolderOptions =
     process.env.NODE_ENV === 'development'
       ? undefined
       : { maxAge: '1y', immutable: true };
 
   if (cluster.isMaster) {
     const didMigrationsSucceed: boolean = await migrate();
     if (!didMigrationsSucceed) {
       // The following line uses exit code 2 to ensure nodemon exits
       // in a dev environment, instead of restarting. Context provided
       // in https://github.com/remy/nodemon/issues/751
       process.exit(2);
     }
     const cpuCount = os.cpus().length;
     for (let i = 0; i < cpuCount; i++) {
       cluster.fork();
     }
     cluster.on('exit', () => cluster.fork());
   } else {
     const server = express();
     expressWs(server);
     server.use(express.json({ limit: '250mb' }));
     server.use(cookieParser());
 
     const setupAppRouter = router => {
       router.use('/images', express.static('images'));
       router.use('/fonts', express.static('fonts'));
       router.use('/misc', express.static('misc'));
       router.use(
         '/.well-known',
         express.static(
           '.well-known',
           // Necessary for apple-app-site-association file
           {
             setHeaders: res =>
               res.setHeader('Content-Type', 'application/json'),
           },
         ),
       );
       router.use(
         '/compiled',
         express.static('app_compiled', compiledFolderOptions),
       );
       router.use('/', express.static('icons'));
 
       for (const endpoint in jsonEndpoints) {
         // $FlowFixMe Flow thinks endpoint is string
         const responder = jsonEndpoints[endpoint];
         const expectCookieInvalidation = endpoint === 'log_out';
         router.post(
           `/${endpoint}`,
           jsonHandler(responder, expectCookieInvalidation),
         );
       }
 
       router.get(
         '/create_version/:deviceType/:codeVersion',
         httpGetHandler(createNewVersionResponder),
       );
       router.get(
         '/mark_version_deployed/:deviceType/:codeVersion',
         httpGetHandler(markVersionDeployedResponder),
       );
 
       router.get(
         '/download_error_report/:reportID',
         downloadHandler(errorReportDownloadResponder),
       );
       router.get(
         '/upload/:uploadID/:secret',
         downloadHandler(uploadDownloadResponder),
       );
 
       // This endpoint should be handled by the mobile app. If the server
       // receives this request, it means that the app is not installed and we
       // should redirect the user to a place from which the app can be
       // downloaded.
       router.get('/invite/:secret', (req, res) => {
+        const { secret } = req.params;
         const userAgent = req.get('User-Agent');
         const detectionResult = detectBrowser(userAgent);
-        const redirectUrl =
-          detectionResult.os === 'Android OS'
-            ? stores.googlePlayUrl
-            : stores.appStoreUrl;
+        let redirectUrl = stores.appStoreUrl;
+        if (detectionResult.os === 'Android OS') {
+          const isSecretValid = inviteSecretRegex.test(secret);
+          const referrer = isSecretValid
+            ? `&referrer=${encodeURIComponent(`utm_source=invite/${secret}`)}`
+            : '';
+          redirectUrl = `${stores.googlePlayUrl}${referrer}`;
+        }
         res.writeHead(301, {
           Location: redirectUrl,
         });
         res.end();
       });
 
       // $FlowFixMe express-ws has side effects that can't be typed
       router.ws('/ws', onConnection);
       router.get('/worker/:worker', webWorkerResponder);
       router.get('*', htmlHandler(websiteResponder));
 
       router.post(
         '/upload_multimedia',
         multerProcessor,
         uploadHandler(multimediaUploadResponder),
       );
     };
 
     // Note - the order of router declarations matters. On prod we have
     // squadCalBaseRoutePath configured to '/', which means it's a catch-all. If
     // we call server.use on squadCalRouter first, it will catch all requests
     // and prevent commAppRouter and landingRouter from working correctly. So we
     // make sure that squadCalRouter goes last
 
     if (landingBaseRoutePath) {
       const landingRouter = express.Router();
       landingRouter.use('/images', express.static('images'));
       landingRouter.use('/fonts', express.static('fonts'));
       landingRouter.use(
         '/compiled',
         express.static('landing_compiled', compiledFolderOptions),
       );
       landingRouter.use('/', express.static('landing_icons'));
       landingRouter.post('/subscribe_email', emailSubscriptionResponder);
       landingRouter.get('*', landingHandler);
       server.use(landingBaseRoutePath, landingRouter);
     }
 
     if (commAppBaseRoutePath) {
       const commAppRouter = express.Router();
       setupAppRouter(commAppRouter);
       server.use(commAppBaseRoutePath, commAppRouter);
     }
 
     if (squadCalBaseRoutePath) {
       const squadCalRouter = express.Router();
       setupAppRouter(squadCalRouter);
       server.use(squadCalBaseRoutePath, squadCalRouter);
     }
 
     const listenAddress = (() => {
       if (process.env.COMM_LISTEN_ADDR) {
         return process.env.COMM_LISTEN_ADDR;
       } else if (process.env.NODE_ENV === 'development') {
         return undefined;
       } else {
         return 'localhost';
       }
     })();
 
     server.listen(parseInt(process.env.PORT, 10) || 3000, listenAddress);
   }
 })();