The order cannot be settled as it is not integrated in planning.

What causes this issue?

In the master record for the sender, the "Integrated Planning..."
indicator has not been set. The sender therefore cannot be settled.

How to fix this error?

Check your entries.
If you want to set the "Integrated Planning..." indicator, you can do so
in the sender master data. The indicator is taken from the project
profile or the order type and is proposed when you create the master
data.
If the sender is a real estate object: Business function
RE_CO_INTEGRATION must be activated for integrated planning and
integrated planning for real estate objects must be activated in the
configuration of the plan version.

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

Error message extract from SAP system. Copyright SAP SE.