Dear @Mostafa_AlBelliehy,
As far as I can judge, you shared a doc in this post
Memory issue when using Coda with a browser - #14 by Mostafa_AlBelliehy
Everyone that opened the doc will be added as a viewer, but doesn’t count in a way that will cost you money.
Myself, I have created a folder where I have placed docs shared with others, so I have there only guest viewers and when someone opens and copies the doc it will be added to their account. Just to simplify for myself, although it doesn’t matter
Please check also this explanation