diff --git a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
index 82b73495..51d6be6e 100644
--- a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
+++ b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
@@ -5,6 +5,7 @@ import org.asamk.signal.manager.api.NotRegisteredException;
 import org.asamk.signal.manager.api.Pair;
 import org.asamk.signal.manager.api.ServiceEnvironment;
 import org.asamk.signal.manager.config.ServiceConfig;
+import org.signal.core.models.ServiceId.ACI;
 import org.asamk.signal.manager.config.ServiceEnvironmentConfig;
 import org.asamk.signal.manager.internal.AccountFileUpdaterImpl;
 import org.asamk.signal.manager.internal.ManagerImpl;
@@ -95,6 +96,23 @@ public class SignalAccountFiles {
         return this.initManager(number, accountPath);
     }
 
+    public Manager initManagerByAci(String aciStr) throws IOException, NotRegisteredException, AccountCheckException {
+        final var aci = ACI.parseOrThrow(aciStr);
+        final var accountPath = accountsStore.getPathByAci(aci);
+        if (accountPath == null) {
+            throw new NotRegisteredException();
+        }
+        final var accounts = accountsStore.getAllAccounts();
+        final var account = accounts.stream()
+                .filter(a -> aciStr.equals(a.uuid()))
+                .findFirst()
+                .orElseThrow(NotRegisteredException::new);
+        if (account.number() == null) {
+            throw new NotRegisteredException();
+        }
+        return this.initManager(account.number(), accountPath);
+    }
+
     private Manager initManager(
             String number,
             String accountPath
diff --git a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
index 24ecae61..c4d042e5 100644
--- a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
+++ b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
@@ -95,23 +95,42 @@ public class MultiAccountManagerImpl implements MultiAccountManager {
     }
 
     @Override
-    public Manager getManager(final String number) {
+    public Manager getManager(final String identifier) {
         synchronized (managers) {
-            final var manager = managers.stream()
-                    .filter(m -> m.getSelfNumber().equals(number))
+            // Try to find already loaded manager by phone number
+            var manager = managers.stream()
+                    .filter(m -> m.getSelfNumber().equals(identifier))
                     .findFirst()
                     .orElse(null);
             if (manager != null) {
                 return manager;
             }
+
+            // Try to load by phone number first
             try {
-                final var newManager = signalAccountFiles.initManager(number);
+                final var newManager = signalAccountFiles.initManager(identifier);
                 managers.add(newManager);
                 return newManager;
-            } catch (IOException | NotRegisteredException | AccountCheckException e) {
-                logger.warn("Failed to load new manager", e);
+            } catch (NotRegisteredException e) {
+                // Not a valid phone number or not registered yet, try ACI
+                logger.debug("Manager not found by number, trying ACI: {}", identifier);
+            } catch (IOException | AccountCheckException e) {
+                logger.warn("Failed to load new manager by number: {}", identifier, e);
                 return null;
             }
+
+            // Try to load by ACI (useful for SSE endpoint with ?account=<UUID>)
+            try {
+                final var newManager = signalAccountFiles.initManagerByAci(identifier);
+                managers.add(newManager);
+                return newManager;
+            } catch (NotRegisteredException e) {
+                logger.debug("Manager not found by ACI: {}", identifier);
+            } catch (IOException | AccountCheckException e) {
+                logger.warn("Failed to load new manager by ACI: {}", identifier, e);
+            }
+
+            return null;
         }
     }
 
diff --git a/src/main/java/org/asamk/signal/http/HttpServerHandler.java b/src/main/java/org/asamk/signal/http/HttpServerHandler.java
index a6fc9f9e..1d2c48f8 100644
--- a/src/main/java/org/asamk/signal/http/HttpServerHandler.java
+++ b/src/main/java/org/asamk/signal/http/HttpServerHandler.java
@@ -262,7 +262,10 @@ public class HttpServerHandler implements AutoCloseable {
             } else {
                 final var manager = c.getManager(account);
                 if (manager == null) {
-                    return null;
+                    // Account not found by the given identifier (number or ACI/UUID)
+                    // Log the available accounts to help debug
+                    logger.warn("Account not found for identifier: {}", account);
+                    return c.getManagers();
                 }
                 return List.of(manager);
             }