Unable to refresh Materialized view manually in Oracle12c

Question

I created a materialized view as show below:

CREATE MATERIALIZED VIEW ORA2ORA_DW.INVOICE_AGG
BUILD IMMEDIATE 
REFRESH FORCE
ON DEMAND
DISABLE QUERY REWRITE 
AS
SELECT C.CUSTOMERID , C.CUSTOMERNAME,  SUM(I.QUANTITY) AS QUANTITY, MAX(I.UNITPRICE) AS UNITPRICE, MIN(I.TAXAMOUNT) AS AMOUNT, 
AVG(I.TAXRATE) AS TAX, VARIANCE(I.LINEPROFIT)AS LINEPROFIT_VAR, STDDEV(I.LINEPROFIT) AS LINEPROFIT_STDEV, COUNT(I.INVOICELINESKEY) AS ROW_COUNT
FROM ORA2ORA_DW.INVOICELINES I, ORA2ORA_DW.CUSTOMERS C
WHERE  I.CUSTOMERSKEY=C.CUSTOMERSKEY
GROUP BY  C.CUSTOMERID , C.CUSTOMERNAME
ORDER BY C.CUSTOMERID;

but when I try to refresh it using this command "EXEC DBMS_MVIEW.REFRESH('INVOICE_AGG');", it gives me this error: ORA-00900: invalid SQL statement