diff --git a/infra/event-sync/src/main/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCase.kt b/infra/event-sync/src/main/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCase.kt
index a130c46137..38fda4066e 100644
--- a/infra/event-sync/src/main/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCase.kt
+++ b/infra/event-sync/src/main/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCase.kt
@@ -19,15 +19,20 @@ internal class TokenizeEventPayloadFieldsUseCase @Inject constructor(
                 project = project,
             )
         }
-        val tokenizedListFields = event.getTokenizableListFields().mapValues { (tokenKeyType, listFieldValue) ->
-            listFieldValue.map { fieldValue ->
-                tokenizationProcessor.tokenizeIfNecessary(
-                    tokenizableString = fieldValue,
-                    tokenKeyType = tokenKeyType,
-                    project = project,
-                )
+        val tokenizedListFields = event
+            .getTokenizableListFields()
+            // Empty lists have nothing to tokenize, and propagating them would replace an absent
+            // field with an empty one that the backend then rejects as untokenized.
+            .filterValues { it.isNotEmpty() }
+            .mapValues { (tokenKeyType, listFieldValue) ->
+                listFieldValue.map { fieldValue ->
+                    tokenizationProcessor.tokenizeIfNecessary(
+                        tokenizableString = fieldValue,
+                        tokenKeyType = tokenKeyType,
+                        project = project,
+                    )
+                }
             }
-        }
         return event.setTokenizedFields(tokenizedFields).setTokenizedListFields(tokenizedListFields)
     }
 }
diff --git a/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/MapDomainEventToApiUseCaseTest.kt b/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/MapDomainEventToApiUseCaseTest.kt
index ac9bfd322a..2238e80ee3 100644
--- a/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/MapDomainEventToApiUseCaseTest.kt
+++ b/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/MapDomainEventToApiUseCaseTest.kt
@@ -639,6 +639,18 @@ internal class MapDomainEventToApiUseCaseTest {
         validateDeviceConfigurationUpdatedApiModel(json)
     }
 
+    @Test
+    fun `when no modules are selected, then downSyncModules should be omitted from the ApiEvent`() {
+        val event = createDeviceConfigurationUpdatedEvent().let {
+            it.copy(payload = it.payload.copy(configuration = it.payload.configuration.copy(downSyncModules = null)))
+        }
+        val apiEvent = useCase(event, project)
+        val json = JSONObject(SimJson.encodeToString(apiEvent))
+
+        assertThat(json.getJSONObject("payload").getJSONObject("configuration").has("downSyncModules")).isFalse()
+        assertThat(json.getJSONArray("tokenizedFields").length()).isEqualTo(0)
+    }
+
     @Test
     fun `when event contains tokenized attendant id, then ApiEvent should contain tokenizedField`() {
         validateUserIdTokenization(attendantId = "attendantId".asTokenizableEncrypted())
diff --git a/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCaseTest.kt b/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCaseTest.kt
index 8681e88490..430a904677 100644
--- a/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCaseTest.kt
+++ b/infra/event-sync/src/test/java/com/simprints/infra/eventsync/event/usecases/TokenizeEventPayloadFieldsUseCaseTest.kt
@@ -61,6 +61,17 @@ internal class TokenizeEventPayloadFieldsUseCaseTest {
         verify { event.setTokenizedListFields(mapOf(tokenKeyTypeList to listOf(tokenizedString, tokenizedString))) }
     }
 
+    @Test
+    fun `should not invoke tokenizeIfNecessary for empty list of TokenizableString`() {
+        every { event.getTokenizableFields() } returns emptyMap()
+        every { event.getTokenizableListFields() } returns mapOf(tokenKeyTypeList to emptyList())
+
+        useCase(event = event, project = project)
+
+        verify(exactly = 0) { tokenizationProcessor.tokenizeIfNecessary(any(), any(), any()) }
+        verify { event.setTokenizedListFields(emptyMap()) }
+    }
+
     @Test
     fun `should handle both field and list of TokenizableString in same event`() {
         every { event.getTokenizableFields() } returns mapOf(tokenKeyType to rawString)
diff --git a/infra/events/src/test/java/com/simprints/infra/events/event/domain/models/DeviceConfigurationUpdatedEventTest.kt b/infra/events/src/test/java/com/simprints/infra/events/event/domain/models/DeviceConfigurationUpdatedEventTest.kt
index 3e5d557ed9..9b430733ff 100644
--- a/infra/events/src/test/java/com/simprints/infra/events/event/domain/models/DeviceConfigurationUpdatedEventTest.kt
+++ b/infra/events/src/test/java/com/simprints/infra/events/event/domain/models/DeviceConfigurationUpdatedEventTest.kt
@@ -1,6 +1,7 @@
 package com.simprints.infra.events.event.domain.models
 
 import com.google.common.truth.Truth.*
+import com.simprints.core.domain.tokenization.TokenizableString
 import com.simprints.core.domain.tokenization.asTokenizableEncrypted
 import com.simprints.core.domain.tokenization.asTokenizableRaw
 import com.simprints.infra.config.store.models.TokenKeyType
@@ -56,13 +57,36 @@ class DeviceConfigurationUpdatedEventTest {
         )
     }
 
-    private fun createDefaultEvent(): DeviceConfigurationUpdatedEvent = DeviceConfigurationUpdatedEvent(
-        createdAt = CREATED_AT,
-        language = "en",
-        downSyncModules = listOf(
+    @Test
+    fun setTokenizableFields_keepsExistingModuleIdsWhenMapHasNoModuleIds() {
+        val event = createDefaultEvent()
+
+        val updatedEvent = event.setTokenizedListFields(emptyMap()) as DeviceConfigurationUpdatedEvent
+
+        assertThat(updatedEvent.payload.configuration.downSyncModules).containsExactly(
+            "module1".asTokenizableRaw(),
+            "module2".asTokenizableEncrypted(),
+        )
+    }
+
+    @Test
+    fun setTokenizableFields_keepsModuleIdsNullWhenMapHasNoModuleIds() {
+        val event = createDefaultEvent(downSyncModules = null)
+
+        val updatedEvent = event.setTokenizedListFields(emptyMap()) as DeviceConfigurationUpdatedEvent
+
+        assertThat(updatedEvent.payload.configuration.downSyncModules).isNull()
+    }
+
+    private fun createDefaultEvent(
+        downSyncModules: List<TokenizableString>? = listOf(
             "module1".asTokenizableRaw(),
             "module2".asTokenizableEncrypted(),
         ),
+    ): DeviceConfigurationUpdatedEvent = DeviceConfigurationUpdatedEvent(
+        createdAt = CREATED_AT,
+        language = "en",
+        downSyncModules = downSyncModules,
         sourceUpdate = DeviceConfigurationUpdatedEvent.DeviceConfigurationUpdateSource.REMOTE,
     )
 }