Cannot add fieldgroups on a subtab

AI generated answer (using internal Slack threads):

Based on the conversations, it appears that you cannot directly add field groups to a custom subtab in NetSuite. However, once you add fields to the custom subtab, the field groups should appear. This is evident from the first thread where the user initially couldn't see the field groups for the custom subtab, but after adding fields and waiting for some time, the field groups appeared. In the second thread, the user was trying to force the header bar of a subtab to show when there is only one subtab on a custom form. The suggestion to add a field group did not work in this case. In the third thread, the user encountered an error when trying to add a file upload field to a field group. The error message indicated that file upload fields cannot be added to tabs, subtabs, sublists, or field groups and are not allowed on existing pages. This is a limitation of the FILE field type in NetSuite. ****** Disclaimer: This response was generated by an artificial intelligence assistant based on previous conversations from multiple Slack channels, and may contain inaccuracies or mistakes. ******