html field not passing data across via api

Afternoon all

Im working on an ServiceNow to ServiceNow integration via Rest API.

I have a field 'implementation plan' on my side which is a string field. On the Customers side the 'Implementation Plan' field is a HTML field.

When i create my record and send via rest api I can pass the text i type into my 'Implementation plan' field  and it appears as it should on there side. So all good.

When the customer creates a record on there side to send across , What they type into there Implementation plan field  doesn't come across, It arrives with 'Undefined' i think. I'm guessing there is a json method i may have to use.

Any suggestions or anyone had the same issue and got a solution. Thanks all.