How to store array parameter of a function to contract state?

Question

I am trying to save an invoice to contract storage (see function addNewInvoice(..)) but I seem to be tripping over the data locations.

// SPDX-License-Identifier: private
pragma solidity >=0.7.0;
pragma experimental ABIEncoderV2;


contract InvoiceValidator {

    mapping(uint => Invoice) private idToInvoiceMap;
    uint[] private invoicesToValidate;
    
    struct Treatment {
        string description;
        uint cost;
    }

    struct Invoice {
        address recipient;
        address sender;
        string patient;
        uint date;
        Treatment[] treatment;
    }

    constructor() {}

    function addNewInvoice(address recipient, address sender, string memory patient, uint date, Treatment[] memory treatments)
    external
    {
        uint invoiceId = 1;
        Invoice memory invoice = Invoice(recipient, sender, patient, date, treatments);
        idToInvoiceMap[invoiceId] = invoice;
        invoicesToValidate.push(invoiceId);
    }
}

throws

UnimplementedFeatureError: Copying of type struct InvoiceValidator.Treatment memory[] memory to storage not yet supported.

I think this is because of the line

idToInvoiceMap[invoiceId] = invoice;

which would save the invoice to contract state, which is what I am trying to do.

Is there a way to achieve this?

Also, I couldn't find a whole lot of good ressources about data location (storage, memory, calldata[, stack]), so I'm not sure if memory is even the right location for the local invoice variable. But if I change the line

Invoice memory invoice = Invoice(recipient, sender, patient, date, treatments);

to

Invoice storage invoice = Invoice(recipient, sender, patient, date, treatments);

the compiler throws

[...].sol:30:9: TypeError: Type struct InvoiceValidator.Invoice memory is not implicitly convertible to expected type struct InvoiceValidator.Invoice storage pointer. Invoice storage invoice = Invoice(recipient, sender, patient, date, treatments); ^-----------------------------------------------------------------------------^

And what I do not understand either is that when I change the Invoice struct treatment property to a single Treatment (instead of an array of them) like this:

struct Invoice {
        address recipient;
        address sender;
        string patient;
        uint date;
        Treatment treatment;
}

and try to assign it like this:

Invoice memory invoice = Invoice(recipient, sender, patient, date, treatments[0]);

it seems to work, but changing to storage

Invoice storage invoice = Invoice(recipient, sender, patient, date, treatments[0]);

throws

[...].sol:30:9: TypeError: Type struct InvoiceValidator.Invoice memory is not implicitly convertible to expected type struct InvoiceValidator.Invoice storage pointer. Invoice storage invoice = Invoice(recipient, sender, patient, date, treatments[0]); ^--------------------------------------------------------------------------------^

So there seems to be another problem with arrays of reference types vs reference type only?

I would much appreciate if somebody could help me solve how to save this invoice containing a list of treatments to contract storage or shine some light on my confusion in general.

(Also: I couldn't find much information about this either but am I correct in assuming that it would be more appropriate to emit events and create an outside-the-blockchain storage to keep track of data instead of storing a lot of invoices inside the contract?)