I think this is because you did not enable CORS at the top of page.
One CORS is enabled, you can define and save all the form's fields.
I keep this issue to disabled fields when CORS is disabled.
changed the title from
CORS cant save customer Access-Control-Allow-Headers,for excample X-Gravitee-Api-Key.
[management-ui] CORS cant save customer Access-Control-Allow-Headers,for excample X-Gravitee-Api-Key.Sep 28, 2018
The CORS is in active.
In Access-Control-Allow-Headers,it seems that can only save the headers which is in the drop down list,
like Content-type,Cache-control and so on.But,cant save the X-Gravitee-Api-Key which is not in the drop down list.