Importing Attendees; association and custom questions

Hi!

I’m trying to use the RSVP plugin for the first time. All is setup, I made 2 custom questions and now I want to import the list of attendees. Thing is, I made a complete excelfile with associated attendees and who should answer which question, but if I import the excelfile (either as .xlsx or .csv), the plugin only seems to register the first name and second name, not the associated attendees or custom questions.
To resolve this issue, I manually entered some attendees with associated attendees and custom questions, exported the list of attendees to get an idea how it should be organized. But even when I deleted the manually entered attendees from the plugin and then imported the exported file, it only registers the first and last name and not associations or custom questions.
I’m using the latest WP and everything is updated. Can someone help me do some troubleshooting?

I’m using WP 6.0 and PHP 8.0.

Twan