How do I enable the function Split/Allocate in the CM25 Capacity Table?

I work in the Processing industry. My MOAP Resource consists of two machines so the capacity detail has “No. of indiv. Cap” = 2 and the flag “Can be used by several operations” is set. See screen shot below.

Usually I run this product on just a single processing unit while another product runs at the same time on the other processing unit. But sometimes I want to run this product on both processing units at the same time to get the job done in half the time. I expect to be able to do an online Split in CM25 using the “Split/Allocate” function but it is greyed out. See screen shot below.

Is there a trick to get this function available? Thank you very much!