update link (#1241)

Author: youssefea

docs/ai-agents/guides/x402-payments.mdx

@@ -230,6 +230,6 @@ You can also build agent services that charge other agents for access using x402
 
 ## Next step
 
-<Card title="Identity with SIWA" icon="arrow-right" href="/ai-agents/guides/identity-siwa">
-  Make your agent discoverable and verifiable so other agents and services can trust it.
+<Card title="Register and Sign In With Agent" icon="arrow-right" href="/ai-agents/guides/register-and-sign-in-your-agent">
+  Register your agent and verify its identity using Sign In With Agent.
 </Card>