Error with attribute not existing

[Cindy Verberkt]

I have ran this script:
Design
;alts = Persoon_A, Persoon_B
;rows = 30
;block = 2
;eff = (rp, d)
;rdraws = mlhs(100)
;rep = 100

;model:

U(Persoon_A) =
b1[n, 0, 1] * risico.a[1,2,3]
+ b2[n, 0.2, 0.3] * ziekenhuisbezoek.a[1,2,3,4]
+ b3[n, 0.15, 0.3] * test.a[1,2,3]
+ b4[n, 0.1, 0.25] * klachten.a[1,2]
+ b5[n, 0.1, 0.2] * hulp.a[1,2]
/
U(Persoon_B) =
b1[n] * risico.b[1,2,3]
+ b2[n] * ziekenhuisbezoek.b[1,2,3,4]
+ b3[n] * test.b[1,2,3]
+ b4[n] * klachten.b[1,2]
+ b5[n] * hulp.b[1,2]

;rand
;require: Persoon_A.risico.a = Persoon_B.risico.b
$

And received this "Error: The ';require' property contains an attribute that does not exist in the design. 'persoon_a.risico.a"
I would like the output for risico.a and risico.b to be the same --> risico.a = 1 and risico.b = 1.

I do not know how to change the script that it does recognise the attributes as it was able to run before adding the require function!