I attach the text of the entire create function instruction, and also of the create table instruction.
The restore is not going to execute functions on its own and you've only shown two create statements. Somewhere else in your dump file the function check_account_from_bill_items must be referenced in order for it to be called. You need to show that. It is not the function creation that is going to be illegal, it will be, like Adrian said, something like using a volatile function in a check constraint that is going to be illegal.
We are working with version 10.23, and I cannot send you the entire output of the pg_dump file because it is 3.3 GB, but am happy to send you any parts that might help.
I doubt a schema-only dump is going to be that large...but you are right that you should be trying harder to isolate this down to a reproducible test case and thus be able to provide more information without it being too much.