cant delete custom field

Hi, yesterday the booking form was working fine with all the input fields showing correctly, but today I have duplicate custom fields with the same slug name. When I try and delete the duplicate it just says “error on deletion” When I change the slug name the duplicate slug name also changes to the updated name and when I change the field to Visible no it still displays it. How can I resolve this problem?
I’m using Easy Appointment V3.5.2

Siggi

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