title: Keras model shape incompatible / ValueError: Shapes (None, 3) and (None, 3, 3) are incompatible
body: <p>I'm trying to train my keras model but shapes are incompatible.
  The error says</p>
  <pre><code>ValueError: Shapes (None, 3) and (None, 3, 3) are incompatible
  </code></pre>
  <p>My train set's shape is (2000, 3, 768) and lable's shape is (2000, 3).</p>
  <p>What is the wrong the point?</p>
  <p>Model define &amp; fit code</p>
  <pre><code>input_shape = x_train.shape[1:]
  model = my_dnn(input_shape, 3)
  model.fit(x_train, y_train, epochs=25, verbose=1)
  </code></pre>
  <p>Model code</p>
  <pre><code>def my_dnn(input, num_classes):
  
      model = Sequential()
      model.add(tf.keras.Input(input))
      model.add(Dense(1024))
      model.add(Activation('relu'))
      model.add(Dropout(0.5))
      model.add(Dense(512))
      model.add(Activation('relu'))
      model.add(Dense(225))
      model.add(Activation('relu'))
      model.add(Dense(100))
      model.add(Activation('relu'))
      model.add(Dense(num_classes))
      model.add(Activation('sigmoid'))
  
  
      model.compile( loss='categorical_crossentropy', 
                     optimizer='adam', 
                     metrics=[tf.keras.metrics.SparseCategoricalAccuracy()])
  
      return model
  </code></pre>