ufunc 'subtract' not supported for the input types....inputs could not be safely coerced to any supported types according to the casting rule ''safe''

Question

import numpy as np
import xpress as xp
p = xp.problem ("Problem")

x = np.empty(6+1).tolist()
constraint = np.array([140,100,110,100,120,100], dtype = xp.npvar)
for i in range(6):
    x[i] = x[i] <= constraint
    p.addConstraint(x[i])
    

y = np.empty(6+1).tolist()
diff =np.array([120,100,90,120,110], dtype = xp.npvar)
for n in range(6):
    if(y[0]):
        y[n] == x[n] - 100
    y[n] == x[n] + y[n] - diff
    p.addConstraint(y[n])

so i was trying to run this code using numpy and xpress and after that I got this error

ufunc 'subtract' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

I dont know what to do right after this, i tried using tempt variables, or declaring them int... and still doesnt change a thing