Can a 400 Bad Request error be caused by invalid characters in the URL when using PowerShell?

Yes, absolutely. URLs have specific rules about allowed characters. Spaces, special characters (like &, ?, #, etc.), and certain Unicode characters need to be properly URL-encoded. PowerShell's `[System.Web.HttpUtility]::UrlEncode()` can be used to encode these characters before including them in the URL. Incorrectly encoded URLs are a common cause of 400 errors.