[Activities] Ammend guide to clarify referrer_id behavior

Author: goatslacker

docs/activities/development-guides.mdx

@@ -888,9 +888,19 @@ This example is being done entirely on the client, however, a more common patter
 
 ### Prompting Users to Share Incentivized Links
 
-Incentivized sharing can help grow your Activity through network effects. This guide covers implementing a reward system for users who share links and those who click them.
+Incentivized sharing can help grow your Activity through network effects. You can use links in several different ways such as:
+
+1. **Referral links.** Users can copy referral links inside your Activity, which include their Discord user ID (`https://discord.com/activities/<your Activity ID>?referrer_id=123456789`), and they can send to their friends. If their friend accepts and starts playing your game, then you gift the referrer something inside your game.
+2. **Promotions.** You can run a temporary promotion on social media, where you offer a reward if they start playing now. Share a custom link on your social media (`https://discord.com/activities/<your Activity ID>?custom_id=social012025` ). Anyone who clicks that specific link receives something inside your game.
+3. **Social deep-links.** Currently, when users launch an Activity, they all land in the same place. Instead, you can start deep-linking to contextually relevant points in your game. For example, user A can copy a link inside your Activity for engaging other users (`https://discord.com/activities/<your Activity ID>?referrer=123456789&custom_id=visit-location`), and sends the link to their friends in a DM or channel. Then, user B who clicks the link gets taken directly to user A’s location.
+4. **Turn-based deep-links.** When you send an “it’s your turn” DM to a user, you can include a link which takes them directly to the right game instance and the turn they need to take.
+5. **Affiliate marketing.** You can work with affiliates (influencers, companies, etc) to advertise your game to their followings, and reward them via a custom link (`https://discord.com/activities/<your Activity ID>?custom_id=influencer1`). Then, for every user that starts playing because of said influencer, you can then pay out to the influencer.
+6. **Source attribution.** You can use the `custom_id` parameter to figure out how much traffic you’re getting from different marketing sources.
+
+This guide covers implementing a referral link which will feature a reward system for users who share links and those who click them.
 
 #### Implementation Overview
+
 1. Create and track an incentivized link for a promotional campaign, then prompt users to share the link
 2. Handle incoming referrals and grant valid rewards
 
@@ -910,7 +920,6 @@ try {
     const { success } = await discordSdk.commands.shareLink({
         message: 'Click this link to redeem 5 free coins!',
         custom_id: customId,
-        // referrer_id is optional - if omitted, the current user's ID is used
     });
 
     if (success) {
@@ -924,6 +933,7 @@ try {
 ```
 
 #### Handling Incoming Referrals
+
 When a user clicks a shared link, your activity will launch with referral data available through the SDK:
 
 ```javascript
@@ -961,10 +971,12 @@ async function handleReferral() {
 ```
 
 #### Link Sharing Best Practices
+
 - Generate unique, non-guessable `customId`s
 - Track and validate referrals to prevent abuse
 - Handle edge cases like expired promotions gracefully
 - Consider implementing cool-down periods between shares
+- Do not override the `referrer_id` query parameter directly. When present, `referrer_id` is expected to be a Discord snowflake-type user ID, otherwise it will be set to the message's author id.
 
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