Table &1 contains more than one entry for &2/&3

What causes this issue?

When calling a function module, more than one entry for the specified
fields was transferred in the specified table yet only one entry is
allowed.

System Response

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

How to fix this error?

Check the call.

Error message extract from SAP system. Copyright SAP SE.