diff --git a/apps/web/app/api/v1/client/[environmentId]/people/[userId]/route.ts b/apps/web/app/api/v1/client/[environmentId]/people/[userId]/route.ts
index 56cab874fb..3e6a6e7ac7 100644
--- a/apps/web/app/api/v1/client/[environmentId]/people/[userId]/route.ts
+++ b/apps/web/app/api/v1/client/[environmentId]/people/[userId]/route.ts
@@ -31,6 +31,9 @@ export async function POST(req: Request, context: Context): Promise<Response> {
       );
     }
 
+    // remove userId from attributes because it is not allowed to be updated
+    const { userId: userIdAttr, ...updatedAttributes } = inputValidation.data.attributes;
+
     let person = await getPersonByUserId(environmentId, userId);
 
     if (!person) {
@@ -40,11 +43,10 @@ export async function POST(req: Request, context: Context): Promise<Response> {
     }
 
     // Check if the person is already up to date
-    const updatedAtttributes = inputValidation.data.attributes;
     const oldAttributes = person.attributes;
     let isUpToDate = true;
-    for (const key in updatedAtttributes) {
-      if (updatedAtttributes[key] !== oldAttributes[key]) {
+    for (const key in updatedAttributes) {
+      if (updatedAttributes[key] !== oldAttributes[key]) {
         isUpToDate = false;
         break;
       }
diff --git a/packages/database/data-migrations/20240408123456_userid_migration/data-migration.ts b/packages/database/data-migrations/20240408123456_userid_migration/data-migration.ts
index af414ca3cf..e80923cc0b 100644
--- a/packages/database/data-migrations/20240408123456_userid_migration/data-migration.ts
+++ b/packages/database/data-migrations/20240408123456_userid_migration/data-migration.ts
@@ -6,55 +6,44 @@ async function main() {
   await prisma.$transaction(
     async (tx) => {
       // get all the persons that have an attribute class with the name "userId"
-      const personsWithUserIdAttribute = await tx.person.findMany({
+      const userIdAttributeClasses = await tx.attributeClass.findMany({
         where: {
-          attributes: {
-            some: {
-              attributeClass: {
-                name: "userId",
-              },
-            },
-          },
+          name: "userId",
         },
         include: {
           attributes: {
-            include: { attributeClass: true },
+            include: { person: true },
           },
         },
       });
 
-      for (let person of personsWithUserIdAttribute) {
-        // If the person already has a userId, skip it
-        if (person.userId) {
-          continue;
-        }
-
-        const userIdAttributeValue = person.attributes.find((attribute) => {
-          if (attribute.attributeClass.name === "userId") {
-            return attribute;
+      for (let attributeClass of userIdAttributeClasses) {
+        for (let attribute of attributeClass.attributes) {
+          if (attribute.person.userId) {
+            continue;
           }
-        });
 
-        if (!userIdAttributeValue) {
-          continue;
+          await tx.person.update({
+            where: {
+              id: attribute.personId,
+            },
+            data: {
+              userId: attribute.value,
+            },
+          });
         }
-
-        await tx.person.update({
-          where: {
-            id: person.id,
-          },
-          data: {
-            userId: userIdAttributeValue.value,
-          },
-        });
       }
 
+      console.log("Migrated userIds to the person table.");
+
       // Delete all attributeClasses with the name "userId"
       await tx.attributeClass.deleteMany({
         where: {
           name: "userId",
         },
       });
+
+      console.log("Deleted attributeClasses with the name 'userId'.");
     },
     {
       timeout: 60000 * 3, // 3 minutes
diff --git a/packages/js-core/src/lib/person.ts b/packages/js-core/src/lib/person.ts
index 391a39c23c..b5a8bf6107 100644
--- a/packages/js-core/src/lib/person.ts
+++ b/packages/js-core/src/lib/person.ts
@@ -147,6 +147,11 @@ export const setPersonAttribute = async (
   key: string,
   value: any
 ): Promise<Result<void, NetworkError | MissingPersonError>> => {
+  if (key === "userId") {
+    logger.error("Setting userId is no longer supported. Please set the userId in the init call instead.");
+    return okVoid();
+  }
+
   logger.debug("Setting attribute: " + key + " to value: " + value);
   // check if attribute already exists with this value
   if (isExistingAttribute(key, value.toString())) {