[SOLVED] GPflow AdamOptimizer issue

I want to use GPflow's AdamOptimizer in my python code.

As mentioned in the previous post, gpflow is working with a certain version of the TensorFlow.

I followed the answer in post, I tried three different combinations inside the virtual environment.

Tensorflow    GPflow
  1.5          1.4
  1.13.0       1.2.0
  1.11.0       1.2.0

I still can't implement:

gpflow.train.AdamOptimizer

Error is: Cannot find the reference in the init.py

Do you have any suggestions for me?

P.S. I think this question is not the duplicate of post, because the answer of that post is not working for me.