DataSHIELD functions are categorised as either aggregate type functions or assign type functions. As a developer, you need to specify which type each of your new functions is. To do this, create the following file within your package:
/inst/DATASHIELD
Now add the following line:
AggregateMethods:
funLevelsDSDS
When you write assign-type functions, the process is the same. For example, you would also add a line:
AggregateMethods:
funLevelsDSDS
AssignMethods:
myAssignFunctionDS