I read that. The field name does exist however, since when I call the function the second time, the fields have already been created.
This causes me to wonder how one could properly write a plugin for deployment having to rely on field keys which may vary from one installation to an other.
I’ve solved the issue myself. I had changed the field keys so they were the same as the field name which was causing a conflict. I’ve changed them back to the standard field_cefffd0f7209b
format.