Shift sequence & is not set up

What causes this issue?

You are attempting to enter shift sequence &V1&. However, shift
sequence &V1& is either not defined or not assigned to the current
grouping from the capacity header.

How to fix this error?

Define shift sequence &V1&, if it does not exist and/or
assign shift sequence &V1& to the current grouping or
enter the appropriate grouping for shift sequence &V1& or
select a shift sequence which is assigned to the current grouping.

Error message extract from SAP system. Copyright SAP SE.