Hello, Mohammad
Welcome to the community.
Not sure If I understood your first question, can you give more details about it?
The payment process for a guest and a observer:
Observers are board members that are able to view a board and the cards within the board, download card attachments, comment and vote on cards (if that is enabled for the board), and export the board. He can be just a guest or a member of the workspace, you can check more details at https://support.atlassian.com/trello/docs/adding-observers-to-boards/
Guests are users who aren't Workspace Members; however, they are members of one or more Boards on Workspace. They aren't able to create Boards, see other Boards in the Workspace, access custom Views, etc. They need to be more tricky regarding the billing question.
Single-Board Guests: Members of one Board of the Workspace (regular users or observers) aren't billed.
Multi-Board Guests: Members who are members of two or more Boards of the Workspace and are billed.
More information about this topic can be found in the articles:
Kind Regards
Alisson
Trello Team
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