BRF+ Formula expression issue

Dear Experts,

Thank you in advance !

I am facing an issue in BRF+ formula calculation. My requirement is to calculate string length of two varialbes and raise error message if length exceeds.

I have created a formula - STR_LNGTH = STRING_LENGTH(LV1) + STRING_LENGTH(LV2)

I have function of ( Event Mode ) and with rule set for processing the formula.

But not getting the desired result in Simulation.

Could you please help on this ?

Warm Regards,

Sharda