Your source systems will often carry crucial information that you want your people to comment on, e.g., financial data (actual vs budget) or HR data (annual leave, turnover), etc.
To enable your system to load data directly onto the appropriate Opal3 indicators, you need to set an identifying code for each of the indicators. The standard names for these codes are "FCode" (for financial indicators) and "NFCode" for non-financial indicators. You should choose sensible codes, e.g., consider using the GL codes from your finance system.
You can allocate the codes individually for each indicator in it's details or settings page, e.g., for new indicators at /admin/indicator/add/...
For financials

For non-financials

... or you can set them for all relevant indicators in bulk (see this article).