Release Strategy on Effective Value not working?

Dear All,

I have configured release strategy for net value + inclusive taxes and I maintained CEKKO-USRN1 in the characteristic.For this Abaper maintained the

USRN1 field in EXIT_SAPLEBND_002. 

But Release Strategy not triggering in purchase order.

Is there any setting required to achieve it.

Kindly guide me on this.

Thanks in advanced.