diff --git a/backend/src/main/java/org/raddatz/familienarchiv/controller/OcrController.java b/backend/src/main/java/org/raddatz/familienarchiv/controller/OcrController.java
index 19f44ab5..a6a65a7b 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/controller/OcrController.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/controller/OcrController.java
@@ -155,7 +155,7 @@ public class OcrController {
     @PostMapping("/api/ocr/train-sender")
     @ResponseStatus(HttpStatus.ACCEPTED)
     @RequirePermission(Permission.ADMIN)
-    public OcrTrainingRun triggerSenderTraining(@RequestBody TriggerSenderTrainingDTO dto) {
+    public OcrTrainingRun triggerSenderTraining(@Valid @RequestBody TriggerSenderTrainingDTO dto) {
         OcrTrainingRun run = senderModelService.triggerManualSenderTraining(dto.personId());
         if (run.getStatus() == TrainingStatus.RUNNING) {
             senderModelService.runSenderTraining(dto.personId());
diff --git a/backend/src/main/java/org/raddatz/familienarchiv/dto/TriggerSenderTrainingDTO.java b/backend/src/main/java/org/raddatz/familienarchiv/dto/TriggerSenderTrainingDTO.java
index baa8d0f3..bae2fcb4 100644
--- a/backend/src/main/java/org/raddatz/familienarchiv/dto/TriggerSenderTrainingDTO.java
+++ b/backend/src/main/java/org/raddatz/familienarchiv/dto/TriggerSenderTrainingDTO.java
@@ -1,5 +1,12 @@
 package org.raddatz.familienarchiv.dto;
 
+import io.swagger.v3.oas.annotations.media.Schema;
+import jakarta.validation.constraints.NotNull;
+
 import java.util.UUID;
 
-public record TriggerSenderTrainingDTO(UUID personId) {}
+public record TriggerSenderTrainingDTO(
+        @NotNull
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+        UUID personId
+) {}
diff --git a/backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java b/backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java
index 236c3d4a..91757d5e 100644
--- a/backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java
+++ b/backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java
@@ -356,6 +356,79 @@ class OcrControllerTest {
                 .andExpect(jsonPath("$.personNames." + personId).value("Anna Müller"));
     }
 
+    // ─── POST /api/ocr/train-sender ───────────────────────────────────────────
+
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void triggerSenderTraining_returns400_whenPersonIdIsNull() throws Exception {
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":null}"))
+                .andExpect(status().isBadRequest());
+    }
+
+    @Test
+    void triggerSenderTraining_returns401_whenUnauthenticated() throws Exception {
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":\"" + UUID.randomUUID() + "\"}"))
+                .andExpect(status().isUnauthorized());
+    }
+
+    @Test
+    @WithMockUser(authorities = "READ_ALL")
+    void triggerSenderTraining_returns403_whenNotAdmin() throws Exception {
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":\"" + UUID.randomUUID() + "\"}"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void triggerSenderTraining_returns404_whenPersonNotFound() throws Exception {
+        UUID unknownId = UUID.randomUUID();
+        when(senderModelService.triggerManualSenderTraining(unknownId))
+                .thenThrow(DomainException.notFound(ErrorCode.PERSON_NOT_FOUND, "Person not found"));
+
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":\"" + unknownId + "\"}"))
+                .andExpect(status().isNotFound());
+    }
+
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void triggerSenderTraining_returns202_withRunning_run() throws Exception {
+        UUID personId = UUID.randomUUID();
+        OcrTrainingRun run = OcrTrainingRun.builder()
+                .id(UUID.randomUUID()).status(TrainingStatus.RUNNING)
+                .personId(personId).blockCount(5).documentCount(0).modelName("sender_" + personId).build();
+        when(senderModelService.triggerManualSenderTraining(personId)).thenReturn(run);
+
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":\"" + personId + "\"}"))
+                .andExpect(status().isAccepted())
+                .andExpect(jsonPath("$.status").value("RUNNING"));
+    }
+
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void triggerSenderTraining_returns202_withQueued_run_whenAnotherRunning() throws Exception {
+        UUID personId = UUID.randomUUID();
+        OcrTrainingRun run = OcrTrainingRun.builder()
+                .id(UUID.randomUUID()).status(TrainingStatus.QUEUED)
+                .personId(personId).blockCount(5).documentCount(0).modelName("sender_" + personId).build();
+        when(senderModelService.triggerManualSenderTraining(personId)).thenReturn(run);
+
+        mockMvc.perform(post("/api/ocr/train-sender")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"personId\":\"" + personId + "\"}"))
+                .andExpect(status().isAccepted())
+                .andExpect(jsonPath("$.status").value("QUEUED"));
+    }
+
     @Test
     @WithMockUser(authorities = "READ_ALL")
     void getDocumentOcrStatus_returnsNone_whenNoOcrJobExists() throws Exception {