On iPhone, when the focus is on a form field, the Safari browser automatically zooms in, remaining in that state and making it difficult to read the conversation.
To avoid this behavior in the window, the viewport of the website where the script is located must contain maximum-scale=1.
On Android devices maximum-scale=1 is not required, but it is recommended to have the viewport correctly configured according to these technical recommendations.
Here is an example of a viewport for iPhone devices: <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" />