Source of supply blocked for this delivery date

What causes this issue?

No purchase orders can be created for this <GL:source_of_supply>source
of supply</> for the delivery date entered because this source is
blocked in the <GL:source_list>source list</> for the material.

How to fix this error?

Try ordering from a different source.
If you really want to procure from this source, you will have to
unblock it in the source list.
<DS:TRAN.ME01>Perform function</>

Error message extract from SAP system. Copyright SAP SE.