diff --git a/src/Config.php b/src/Config.php
index 25474b5a..e79a0a2f 100644
--- a/src/Config.php
+++ b/src/Config.php
@@ -291,13 +291,14 @@ protected function updateConfig(array $config): void
         $this->setLogPayloadLogger($config);
         $this->setVerbose($config);
         $this->setVerboseLogger($config);
+        // The sender must be set before the access token, so we know if it is required.
+        $this->setSender($config);
         $this->setAccessToken($config);
         $this->setDataBuilder($config);
         $this->setTransformer($config);
         $this->setMinimumLevel($config);
         $this->setReportSuppressed($config);
         $this->setFilters($config);
-        $this->setSender($config);
         $this->setScrubber($config);
         $this->setBatched($config);
         $this->setBatchSize($config);
@@ -337,8 +338,14 @@ private function setAccessToken(array $config): void
         if (isset($_ENV['ROLLBAR_ACCESS_TOKEN']) && !isset($config['access_token'])) {
             $config['access_token'] = $_ENV['ROLLBAR_ACCESS_TOKEN'];
         }
-        $this->utilities()->validateString($config['access_token'], "config['access_token']", 32, false);
-        $this->accessToken = $config['access_token'];
+        
+        $this->utilities()->validateString(
+            $config['access_token'],
+            "config['access_token']",
+            32,
+            !$this->sender->requireAccessToken(),
+        );
+        $this->accessToken = $config['access_token'] ?? '';
     }
 
     private function setEnabled(array $config): void
diff --git a/src/Senders/AgentSender.php b/src/Senders/AgentSender.php
index 06ef775d..285c742b 100644
--- a/src/Senders/AgentSender.php
+++ b/src/Senders/AgentSender.php
@@ -60,9 +60,23 @@ public function wait(string $accessToken, int $max): void
         return;
     }
 
+    /**
+     * Returns true if the access token is required by the sender to send the payload. The agent can be configured to
+     * provide its own access token. But may not have its own, so we are requiring it for now. See
+     * {@link https://github.com/rollbar/rollbar-php/issues/405} for more details.
+     *
+     * @since 4.0.0
+     *
+     * @return bool
+     */
+    public function requireAccessToken(): bool
+    {
+        return true;
+    }
+
     private function loadAgentFile()
     {
-        $filename = $this->agentLogLocation . '/rollbar-relay.' . getmypid() . '.' . microtime(true) . '.rollbar';
+        $filename       = $this->agentLogLocation . '/rollbar-relay.' . getmypid() . '.' . microtime(true) . '.rollbar';
         $this->agentLog = fopen($filename, 'a');
     }
 }
diff --git a/src/Senders/CurlSender.php b/src/Senders/CurlSender.php
index 0df74309..4994827a 100644
--- a/src/Senders/CurlSender.php
+++ b/src/Senders/CurlSender.php
@@ -110,6 +110,18 @@ public function wait(string $accessToken, int $max = 0): void
         }
     }
 
+    /**
+     * Returns true if the access token is required by the sender to send the payload. The curl sender requires the
+     * access token since it is sending directly to the Rollbar service.
+     *
+     * @return bool
+     * @since 4.0.0
+     */
+    public function requireAccessToken(): bool
+    {
+        return false;
+    }
+
     private function maybeSendMoreBatchRequests(string $accessToken)
     {
         $max = $this->maxBatchRequests - count($this->inflightRequests);
diff --git a/src/Senders/FluentSender.php b/src/Senders/FluentSender.php
index ddae224c..11f9612c 100644
--- a/src/Senders/FluentSender.php
+++ b/src/Senders/FluentSender.php
@@ -101,6 +101,18 @@ public function wait(string $accessToken, int $max): void
         return;
     }
 
+    /**
+     * Returns true if the access token is required by the sender to send the payload. The Fluentd service can provide
+     * its own access token.
+     *
+     * @return bool
+     * @since 4.0.0
+     */
+    public function requireAccessToken(): bool
+    {
+        return false;
+    }
+
     /**
      * Loads the fluent logger
      */
diff --git a/src/Senders/SenderInterface.php b/src/Senders/SenderInterface.php
index a705633f..395ffc60 100644
--- a/src/Senders/SenderInterface.php
+++ b/src/Senders/SenderInterface.php
@@ -44,4 +44,13 @@ public function sendBatch(array $batch, string $accessToken): void;
      * @return void
      */
     public function wait(string $accessToken, int $max): void;
+
+    /**
+     * Returns true if the access token is required by the sender to send the payload. In cases where an intermediary
+     * sender is being used like Fluentd.
+     *
+     * @return bool
+     * @since 4.0.0
+     */
+    public function requireAccessToken(): bool;
 }
diff --git a/tests/ConfigTest.php b/tests/ConfigTest.php
index b7b8e0b5..3e158286 100644
--- a/tests/ConfigTest.php
+++ b/tests/ConfigTest.php
@@ -428,11 +428,14 @@ public function testFilter(): void
     public function testSender(): void
     {
         $p = m::mock(EncodedPayload::class);
-        $sender = m::mock(SenderInterface::class)
-            ->shouldReceive("send")
+        $sender = m::mock(SenderInterface::class);
+        $sender->shouldReceive("send")
             ->with($p, $this->getTestAccessToken())
             ->once()
             ->mock();
+        $sender->shouldReceive('requireAccessToken')
+            ->once()
+            ->mock();
         $c = new Config(array(
             "access_token" => $this->getTestAccessToken(),
             "environment" => $this->env,
diff --git a/tests/FluentTest.php b/tests/FluentTest.php
index 8438ca35..7272ac33 100644
--- a/tests/FluentTest.php
+++ b/tests/FluentTest.php
@@ -28,7 +28,7 @@ public function testFluent(): void
             'fluent_port' => $port,
             'handler' => 'fluent'
         ));
-        $this->assertEquals(200, $logger->log(Level::INFO, 'this is a test', array())->getStatus());
+        $this->assertEquals(200, $logger->report(Level::INFO, 'this is a test', array())->getStatus());
 
         socket_close($socket);
     }