AMP error: External stylesheets not supported

I am getting below error on many pages of my wordpress website.
Can anyone help me with the clue to solve these errors

External stylesheets not supported, except for whitelisted font providers. Use the document inline ‘style amp-custom’ tag instead

Here is link to few of the pages

https://www.datatobiz.com/2018/07/14/data-science-business-problems/amp/
https://www.datatobiz.com/2019/12/13/face-recognition-on-jetson-nano/amp/
https://www.datatobiz.com/2019/10/03/fixing-wifi-connectivity-nvidia-jetson-nano/amp/
https://www.datatobiz.com/2020/01/28/advantages-machine-learning/amp/

The page I need help with: [log in to see the link]