How call a `@guvectorize` inside a `@guvectorize` in numba?

I'm trying to call a @guvectorize inside a @guvectorize but I have an error saying :

Untyped global name 'regNL_nb': cannot determine Numba type of <class 'numpy.ufunc'>

File "di.py", line 12:
def H2Delay_nb(S1, S2, R2):
    H1 = regNL_nb(S1, S2)
    ^

here is an MRE:

import numpy as np
from numba import guvectorize, float64, int64, njit, cuda, jit

@guvectorize(["float64[:], float64[:], float64[:]"], '(n),(n)->(n)')
def regNL_nb(S1, S2, h2):
    for i in range(len(S1)):
        h2[i] = S1[i] + S2[i]

@guvectorize(["float64[:], float64[:],  float64[:]"], '(n),(n)->(n)',nopython=True)
def H2Delay_nb(S1, S2, R2):
    H1 = regNL_nb(S1, S2)
    H2 = regNL_nb(S1, S2,)
    for i in range(len(S1)):
        R2[i] =  H1[i] + H2[i]


S1 = np.array([1,2,3,4,5,6,7,8,9])
S2 = np.array([1,2,3,4,5,6,7,8,9])
H2 = H2Delay_nb(S1, S2)
print(H2)

I don't know how do I tell to numba that the function regNL_nb is a guvectorize function.

from How call a `@guvectorize` inside a `@guvectorize` in numba?