Communication error calling SAP BW system

What causes this issue?

A communication error between APO and BW occurred during the attempt to
access the Business Information Warehouse (BW).

How to fix this error?

Make sure the correct RFC destination has been assigned and that the BW
in which the KPIs are stored has been correctly set up. RFC
destinations and the BW destination for the KPIs are maintained in
Customizing: (APO IMG -> Supply Chain Cockpit -> Supply Chain Cockpit
-> Key Performance Indicators)
Make sure the R/3 connection for the RFC call was created. The R/3
connection to BW is created in transaction SM59 and must be entered as
the BW default destination in Customizing. (Same menu path as above.)
If a single KPI has different RFC (BW) destinations, they must be
maintained individually in customizing.

Error message extract from SAP system. Copyright SAP SE.