The SUM function only accepts a column reference as an argument.

wdx223_Daniel  Currently I started learning Power BI by doing some beginner level project  which is available from youtube while doing the project I also faced the same problem and found the work around solution for that 

Try this formula I think It would work because it worked for me 

Loss Ratio = Divide(sum(WORK_ADD_OL_DATA[AUTO_LOSS]),SUM(WORK_ADD_OL_DATA[AUTO_EP]),0)