ValueError in Keras: How could I get the model fitted?

I think the problem is that you passed to your model an entire pandas dataset together with the columns headers and an index column. In order to train your model on your data, convert it to a numpy array first with X_train2.values and y_train2.values since a Keras model accepts as input a numpy array and not a pandas dataset

Similar question
Pandas DataFrame and Keras

Documentation on Keras' Sequential model
https://keras.io/models/sequential/

Edit to answer the comments
Don't convert each column separately, this is pointless. Assuming that you have a general dataset df with a column called labels what you have to do is

labels = df.pop("labels")
model.fit(x=df.values, y=labels.values)