This error means that OData cannot parse a valid model instance from the request payload. Check for any missing required (non-nullable) properties or wrong type (string instead of number or vice versa).
it is the standard add form by using this method of a new formdata does not include all the data ? all fields except for the id ( its a new record ) are nullable .
I am pasing the ${event} in the submit
pasing the formData , has same effect
Did you modify the form in any way? Was it working before the modification?
if I take away all the modifications mentioned in your suggested post : calculated fields , the form works
formData contains only the to be calculated fields :
{aantal:1.0,eenheidprijs:0.0,bedrag:0.0,totaalregel:0.0}
But the form has more fields
Are you trying to post more fields than the C# model has? This won't work.
no , that is not the case:
there is one thing might be it : I have changed a string field to lookup
and ddEenheid has value : ${[{text: 'Korting',value:'korting'},{text:'Bonus',value:'bonus'},{text:'Jaar',value:'jaar'},{text:'Hectare',value:'ha'},{text: 'Meter',value: 'm'},{text: 'Stuks',value: 'stuk'}]}
I don't know what eeheid is but the default value seems incorrect. Shouldn't it be lowercase "korting"? That's how it is declared in the ddEenheid: [{text: 'Korting',value:'korting'},
Eenheid: unity
it is a string field in de database accepting varchar(30) , but if the default value is incorrect .. it should display nothing ?
changed to lowercase, no change still 400 bad request .
should this be set
and submit
I am completely lost to be honest. I no longer understand what the latest issue you are discussing is. The thread started about using computed fields, then you said the form fails to save, then that it fails when you use the code from the other thread and finally that it is the dropdown. I cannot guess what is going on unless I reproduce the error locally.
It is the same issue: compute fields on a " add new record" form , the fields are now responding to change so computing , but the form doesn't save to the database
nothing special , just followed the link you provided and ended up in bad request .
Sorry but it is also confusing for me.
@korchev
Found the issue :
uppercase on one database field, somehow someone has mistakenly changed the database field to start with an Uppercase character. most likely it was me 
Field in database : Aantal , Field in Form : aantal.
If the submitted form contained wrong case in fieldnames, I got the Bad Request (400) back.
@korchev :
Would it be strange to ask why the oData request body binding is not case insensitive ?
Positive about this whole issue is that I have learned more on how to debug and troubleshoot.
OData should be case insensitive in terms of JSON parsing. What could have happened though is that Radzen has generated Entity Framework code that wasn't using the right casing. In the future if you rename a column or update a table make sure to infer the database again in Radzen.
In between the time I had this problem with this form , I have made many database changes and infered the database in Radzen.
Could we reproduce this by renaming the column again with Uppercase name, do you expect that it would work ?
No, I couldn't reproduce this issue with MSSQL. I ran a Radzen application and while it was running I renamed a DB column. Both the Add and Edit pages worked as expected. What database are you using?