Resolved: error in saving a cnn model

model = tf.keras.models.Sequential()
model.add(Conv2D(filters=32, kernel_size=(3,3), activation='relu', input_shape=[256,256,3]))
model.add(tf.keras.layers.MaxPool2D(pool_size = (2,2)))
model.add(tf.keras.layers.Flatten())
model.add(tf.keras.layers.Dense( units=128,activation='relu'))
model.add(tf.keras.layers.Dense(4, activation='softmax'))
model.compile(optimizer='adam', loss='categorical_crossentropy', metrics=['accuracy'])

history = model.fit(train_gen,
          epochs=20,
          verbose=1
)

model.save("rock-paper-scissors-model.h5")

AND IT IS SHOWING THIS ERROR

NotImplementedError: Layer ModuleWrapper has arguments in `__init__` and therefore must override `get_config`.