problem with DCchoice package for Double Bounded Ddichotomous Choice (DBDC)

[Ana_kin05]

HI,
I need to do an WTP estimation using Double Bounded Ddichotomous Choice method (DBDC) where bid1, bidh and bidl is fixed. for instance, during the SP survey, the question was- if you are WTP bid1= 1000euro? if yes, then are you WTP bid2= 2000euro? If no, are you WTP bid2 = 500euro? And, bid1= 1000 euro, bidh = 2000euro and bidl = 500euro remains the same. There are 600 entries in the dataset.

The data shows like this-

bid1 bidh bidl answers age sex incomeW ans1 ans2 bid2
1 1000 2000 500 nn 2 1 1 0 0 500
2 1000 2000 500 ny 1 1 2 0 1 500
3 1000 2000 500 ny 3 1 2 0 1 500

I am getting the following error-

Error in optim(ini, fn = dbLL, method = "BFGS", hessian = TRUE, dvar = yvar, :
initial value in 'vmmin' is not finite
In addition: Warning message:
glm.fit: algorithm did not converge

The code looks like this-

library(DCchoice)
library(Ecdat)
library(lmtest)
library(Icens)

if(getRversion() >= "3.6.0") RNGkind(sample.kind = "Rounding")

WTPdata <- read.csv("WTP2.csv")

head(WTPdata, n = 3)


dbnew <- dbchoice(ans1 + ans2 ~ 1 + age + sex + incomeW | bid1 + bid2, dist = "logistic", 
                    data = WTPdata)

I am new to use R. Would it be possible to indicate me where is the problem and how can I solve it?

Thanking you in advance.