Error: The report chart is not available because the running user doesn't have access to a field used for grouping or aggregation

This error is generated when the Source Report used in the Report Chart contains invalid filters or references fields that are not accessible to the running user based on their Field Level Security (FLS) permissions. To resolve the error, follow these steps:

1. Navigate to the source report.
2. Remove any filters from the report.
3. Add the required field to the report, ensuring that your affected user(s) have access to this field via Field Level Security.
4. Save changes to your source report.
5. Refresh the Report Chart on the record detail page.

After completing these steps, the report chart should display without any error messages.