A 422 is typically sent back when
- There are no custom forms on the record you are updating (in this case you will get a message like category cannot be null)
- 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.
![Screenshot 2023-06-07 at 7.25.24 AM.png Screenshot 2023-06-07 at 7.25.24 AM.png](https://experienceleaguecommunities.adobe.com/t5/image/serverpage/image-id/58660iBFAAFD20BDF362B7/image-size/large?v=v2&px=999)