API Form Submit FIELD_NOT_IN_FORM_DEFINITION

I get the following error message when i submit a own hosted test form with the API.

message":"Error in 'fields.i_m_a_'. Field 'i_m_a_' isn't in form definition","errorType":"FIELD_NOT_IN_FORM_DEFINITION"}

'fields' => [

 [....],
 [
 'name' => 'i_m_a_',
 'value' => 'Other'
 ],		
 ],

i_m_a_ ist set as property and is the right “internal name” and the value is one of four option.
Where is the error?!

Hey @GDillenberg
This error means that you’ve not yet added the property into the HS form. A while back HS updated the API to require that all properties submitted are part of the HS form or it will error. I would check your form in the HS editor to ensure that the property is present or that you’ve added the correct property.
Hope this gets you moving

Thx Kevin! But I don’t have a HS form. I want to save the data from an own form additionally in HS. It is a Non-HubSpot form.
I use this api url and it works but not with the i_a_m_ property

//api.hsforms.com/submissions/v3/integration/submit/2697xxxxx/04198c7e-xxx-xxx-bdxxx71-xxxxx

@GDillenberg Oh interesting!
I’m wondering if you’ve updated the form that HubSpot is not liking the modification. Maybe @Anton has any insight?

@GDillenberg Just ran across this as well
https://community.hubspot.com/t5/Developer-Announcements/Amendment-to-Forms-API-Submission-Validation/td-p/782911

Well, i use the secure endpoint and i works out of the box.

api.hsforms.com/submissions/v3/integration/secure/submit