How much is the fine for knocking on the bay window?

It is not illegal to break a bay window. According to China's current laws and regulations, property companies have no right to impose fines on owners, and owners also have the right to refuse. It is illegal for a property company to impose a fine.

Article 39 of the Measures for the Administration of Interior Decoration of Residential Buildings, if buildings and structures are erected in the interior decoration activities of residential buildings without the approval of the competent department of urban planning administration, or the facade of residential buildings is changed without authorization, and doors and windows are opened on the non-load-bearing exterior walls, the competent department of urban planning administration shall punish them in accordance with the provisions of the urban planning law and relevant laws and regulations.