SQLSTATE[23505]: Unique violation in different tables

Hello. I've defined two tables users and user_confirmation_codes but I'm having this input when there is an insert

"SQLSTATE[23505]: Unique violation: 7 ERROR: Duplicate key violates unique constraint «users_idx_unique»\

The problem is that I need in both tables that the idx is unique but in those tables.

Why am I getting this error (Unique violation: 7 ERROR: ) if they are different tables?

user_confirmation_codes

return new class extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('user_confirmation_codes', function (Blueprint $table) {
            $table->id();
            $table->bigInteger('idx')->unique();
            $table->integer('code');
            $table->timestamp('created_at')->nullable();

        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('user_confirmation_codes');
    }
};

users:

return new class extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
              
            $table->id();
            $table->bigInteger('idx')->unique();
            $table->string('name');
            $table->string('email');
            $table->string('password');

            $table->timestamp('email_verified_at')->nullable();

            $table->rememberToken();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('users');
    }
};

This is the controller method:

public function singup(Request $request)
    {

        try {
            $validated = $this->validate($request, [
                'idx' => 'required',
                'name' => 'required',
                'email' => 'required',
                'password' => 'required',
            ]);

            $user = new User();
            $user->idx = $validated['idx'];
            $user->name = $validated['name'];
            $user->email = $validated['email'];

            $user->password = bcrypt($validated['password']);
            $user->save();

            $code = random_int(1000,9999);
            $validation_code = new UserConfirmationCode();
            $validation_code->idx = $validated['idx'];
            $validation_code->code = $code;

            $validation_code->created_at = Carbon::now()->timestamp;
            $validation_code->save();

            Mail::to('[email protected]')
            ->cc('[email protected]')
            ->queue((new EmailConfirmation($user , $code))->from('[email protected]', 'Laravel'));

            return response()->json([
                'status' => true,
                'message' => 'Email Sent',
            ], 201);

        } catch (\Throwable $th) {
            return response()->json([
                'status' => false,
                'message' => $th->getMessage()
            ], 500);
        }

    }