There is no currently supported embed code for Instagram (from the company directly) at this time. Any embed codes will have to come from a third-party source beyond Instagram.
If the Custom HTML script has been provided by a party other than CivicPlus, Support will only be able to assess the interaction of the code with the CMS. Support is unable to troubleshoot third-party code beyond basic analysis.
Please reference our Add HTML on a Page article for more information on adding the code.