No suitable source of supply for product &1 in location &2 found

What causes this issue?

The system has not found a valid source of supply (production data
structure or PPM) for in-house production product &V1& in location &V2&.

System Response

If you have specified in the planning version that the system can only
create a planned order with a source of supply, the system does not
create a planned order.
If you have specified in the planning version that the system can
create a planned order even without a source of supply, the system
creates a planned order.

How to fix this error?

If you want the system to create a planned order with a source of
supply, the following conditions must be fulfilled:
A source of supply exists for products produced in-house, that is,
a production data structure or an active plan.
The source of supply is assigned to the model in which the current
planning version exists.
The source of supply is valid on the requirements date and for the
requirement quantity.

Procedure for System Administrators

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.