diff --git a/.changeset/appauth-registration-response.md b/.changeset/appauth-registration-response.md
new file mode 100644
index 000000000..50b96a433
--- /dev/null
+++ b/.changeset/appauth-registration-response.md
@@ -0,0 +1,5 @@
+---
+"react-native-app-auth": patch
+---
+
+Convert Android dynamic-registration epoch seconds to milliseconds before date formatting. Return the iOS registrationClientUri as its absolute URL string rather than an NSURL object that cannot cross the JSON bridge.
diff --git a/packages/react-native-app-auth/android/src/main/java/com/rnappauth/utils/RegistrationResponseFactory.java b/packages/react-native-app-auth/android/src/main/java/com/rnappauth/utils/RegistrationResponseFactory.java
index 778f5e239..38ce5a9b0 100644
--- a/packages/react-native-app-auth/android/src/main/java/com/rnappauth/utils/RegistrationResponseFactory.java
+++ b/packages/react-native-app-auth/android/src/main/java/com/rnappauth/utils/RegistrationResponseFactory.java
@@ -5,6 +5,8 @@
 
 import net.openid.appauth.RegistrationResponse;
 
+import java.util.concurrent.TimeUnit;
+
 public final class RegistrationResponseFactory {
     /*
      * Read raw registration response into a React Native map to be passed down the bridge
@@ -16,7 +18,7 @@ public static final WritableMap registrationResponseToMap(RegistrationResponse r
         map.putMap("additionalParameters", MapUtil.createAdditionalParametersMap(response.additionalParameters));
 
         if (response.clientIdIssuedAt != null) {
-            map.putString("clientIdIssuedAt", DateUtil.formatTimestamp(response.clientIdIssuedAt));
+            map.putString("clientIdIssuedAt", DateUtil.formatTimestamp(TimeUnit.SECONDS.toMillis(response.clientIdIssuedAt)));
         }
 
         if (response.clientSecret != null) {
@@ -24,7 +26,7 @@ public static final WritableMap registrationResponseToMap(RegistrationResponse r
         }
 
         if (response.clientSecretExpiresAt != null) {
-            map.putString("clientSecretExpiresAt", DateUtil.formatTimestamp(response.clientSecretExpiresAt));
+            map.putString("clientSecretExpiresAt", DateUtil.formatTimestamp(TimeUnit.SECONDS.toMillis(response.clientSecretExpiresAt)));
         }
 
         if (response.registrationAccessToken != null) {
diff --git a/packages/react-native-app-auth/ios/RNAppAuth.m b/packages/react-native-app-auth/ios/RNAppAuth.m
index c48163427..c6920e085 100644
--- a/packages/react-native-app-auth/ios/RNAppAuth.m
+++ b/packages/react-native-app-auth/ios/RNAppAuth.m
@@ -643,7 +643,7 @@ - (NSDictionary*)formatRegistrationResponse: (OIDRegistrationResponse*) response
              @"clientSecret": response.clientSecret ? response.clientSecret : @"",
              @"clientSecretExpiresAt": response.clientSecretExpiresAt ? [dateFormat stringFromDate:response.clientSecretExpiresAt] : @"",
              @"registrationAccessToken": response.registrationAccessToken ? response.registrationAccessToken : @"",
-             @"registrationClientUri": response.registrationClientURI ? response.registrationClientURI : @"",
+             @"registrationClientUri": response.registrationClientURI ? response.registrationClientURI.absoluteString : @"",
              @"tokenEndpointAuthMethod": response.tokenEndpointAuthenticationMethod ? response.tokenEndpointAuthenticationMethod : @"",
              };
 }