PT/CT factor could not be calculated

What causes this issue?

One of the factors required to calculate the PT/CT ratio could not be
calculated. The factors calculated are primary voltage &V1&, secondary
voltage &V2&, primary current &V3&, and secondary current &V4&.
This error is normally caused by a transformer group that has been
structured incorrectly.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Check the transformer group.

Error message extract from SAP system. Copyright SAP SE.