What does [422] Invalid Parameter really mean?

[GregWi]

I'm using standard fields (large text) and picklist and trying to map values from the custom fields on a custom Issue form to the same custom fields on a custom Project form - and whether adding to a data structure used in a Create JSON step, or directly mapping from the webook data to the fields in a Update Record module I am getting a 422 error - whether that value is present, or even null.

It sounds like 422 is Workfront's way of saying I get what you are asking me and it looks to be correctly structured, but I don't like / understand it? Why would this be happening - we have lots of other text fields that map just fine.... but not these three.

Super frustrating when there's an error, but no solution provided. And search hasn't helped either - so maybe the community can :-)

[JacquelynMi1]

It would be great if someone from Workfront (or just someone with more knowledge than me) could answer this as I have the same question & the documentation for Fusion is sorely lacking.

[Pete-Worth]

A 422 is typically sent back when 

1.  There are no custom forms on the record you are updating (in this case you will get a message like category cannot be null)
2.  The field is a dropdown/radio/list and the value you are sending does not exist (in this case you will get a message like Invalid Parameter: [The field] value "[the value]"

If there is a form on the record, but the field is not on that form, you will see a 403 with a message like 'X cannot be edited as it is not available on any custom form on this Project'

The information is being returned in Fusion in the error: you'll see it and should have enough information to check the custom form, check the field and then check the value you are trying to send exists

Below example - Field 'Is this a resubmission' does not have a value for 'Maybe' to update: only Yes or No, so a 422 is returned.