Add custom profile fields via auth_email_signup

Hi,

I want to ask about the auth_email_signup web service

I'm using auth_email_signup but I can't add custom profile fields

I look and write code like API Documentation but it doesn't work

moodlewsrestformat:json
wstoken:xxxxxxxxxxxxxxxxxxxxxxxx
wsfunction:auth_email_signup_user

username:johndoe
firstname:John
lastname:Doe
password:xxxxxxx
email:johndoe@mail.local
city:London
country:EN

customprofilefields[0][type]:foo
customprofilefields[0][name]:Foo
customprofilefields[0][value]:Sample

I'm using moodle 3.9 and I'm using Postman for testing

I'm getting an error message:

{"exception":"invalid_parameter_exception","errorcode":"invalidparameter","message":"Invalid parameter value detected (Invalid fieldFoo)","debuginfo":"Invalid fieldFoo"}

Can anyone help me with this problem?

Thank You!