it seems you have created that content type in a different site and trying to use it in another. In such cases it is better to create the content type in 'contentTypeHub' site collection and then publish it for use in other site collection in same tenant.
Please go to https://.sharepoint.com/sites/contentTypeHub/_layouts/15/mngctype.aspx
and then create your new content type. Once the content type is created, open the settings page and publish it. It should be available to your all other sites within few hours.