Hint: Make sure to use UTF-8 as input encoding for all transferred data. Otherwise the chance for misinterpreted characters is given.

The fieldname must contain at least 3 and at most 64 characters. It must not be equal to one of the standard field names or one of the following strings:

The Maileon API supports accessing custom contact fields via API. For custom contact fields, the same limitations are valid as for standard contact fields, which are:

Fieldtype Remark
string The length must not exceed 255 characters.
date Allowed patterns: yyyy-MM-dd and yyyy-MM-dd HH:mm:ss
boolean Allowed values are: true and false
integer Integer numbers are limited to 32 bit values
float 64 bit signed floating point number (compare with double datatype in Java)