Hi,
Please try adding a listing as a new user and test again. Also, check if you have this feature turned off: How to restrict selling to specific listing categories - HivePress Help Center, as there may be no price extras fields at the time of listing creation.
Additionally, please copy this snippet similarly to this topic Add extra price to listing attributes - #14 by yevhen and add it using this doc: How to add custom code snippets - HivePress Help Center.
I hope this is helpful to you.