I found this behavior strange with the REST.
If a UDF was of string with x(max) then trying to create a quote record with REST would not work if I tried to pass in any more than 6 characters for that field.
When I changed it to x(16000) I was able to add more characters and complete the REST call successfully. Seems like the REST oData call did not like that field being x(max). That’s the only thing I changed and I’m now able to create records with data in that field.
Maybe this bit of info might be helpful to someone else.
