[Plugin: Redirect by Custom Field] not working

I installed the plugin, made a post and made a custom field with label redirect and the value with an url. Saved the post and then the custom field was empty again. Tried it many times, with same result. ANd yes, the plugin is installed and activated. Checked that one, because I thought myself that maybe I missed a step there.

https://www.ads-software.com/extend/plugins/redirect-by-custom-field/