Custom Attributes value field

Create a custom event field instead of a custom event attribute (a custom event attribute is a multi-line field). See the documentation here: https://wp-events-plugin.com/documentation/event-attributes/

Thank you! Just what I need.

Unfortunately even after activating the custom fields and clearing the cache, the option does not show in the event. Probably a problem of theme or plugin compatibility. But this I can hopefully solve.

See the following thread to see how to edit the format of the single event page: https://www.ads-software.com/support/topic/some-odd-features-showing-on-my-event-page/. You can then insert your custom attribute (e.g., #_ATT{MYTEXTFIELD}).