TOPIC: Custom field only in billing page

Is possible to configure custom fields for both registration types(Indidual and group) but show only on billing form?

Of course. You can set this both for the default settings of the field as well as specific to any event. Set the field to be used for both individual and group. Then to the right you'll see more options that are for group registrations only. You can set a field for Each Member, Billing page, or Members & Billing. This is where you need to set it as needed. Check the video tutorials for more info and further explanation.

Not works for me, here my configs.

All Events: Yes
Show: Both
Required: Yes
Group Registrations: Billing Only

When I click on register and select one of registration groups, that field is showed for me.

Obs.: My DT version is 2.7.1

After modifying your field, re-save the event so the new default settings are applied to the event. That is, if the event is even using the default settings. Second thing is you REALLY need to upgrade. We do not support 2.7.1 at all.

With a current package and properly set fields, this will most definitely work correctly.