Why am I not allowed on an open-grouped invoice record to change custom body or sublist field value on an invoice that is grouped, getting this error: FIELDS_1_CANNOT_BE_CHANGED_AFTER_INVOICE_IS_GROUPED

AI generated answer (using internal Slack threads):

The error 'FIELDS_1_CANNOT_BE_CHANGED_AFTER_INVOICE_IS_GROUPED' is thrown when you try to modify certain fields on an invoice that is part of a group. This is due to the fact that NetSuite has certain restrictions on modifying grouped invoices. When an invoice is part of a group, NetSuite treats it as a single entity with the other invoices in the group. This is done to maintain consistency and integrity of the data. Therefore, certain fields, including custom body or sublist fields, cannot be changed once the invoice is grouped. This is a built-in behavior of NetSuite and cannot be changed. If you need to modify these fields, you would need to ungroup the invoice, make the changes, and then regroup it. However, be aware that this could have other implications on your data and processes, so it should be done with caution. ****** Disclaimer: This response was generated by an artificial intelligence assistant based on previous conversations from multiple Slack channels, and may contain inaccuracies or mistakes. ******