Force required product into cart

When a customer adds a specific product to the cart, I need to force an additional product to the cart.

The "kit" functionality in Squarespace isn't really a kit... it functions as a bundle.  In other words, we can define a kit as a product with one or more sub-components, but when added to the cart, the kit appears as a single line item on the invoice.  We need a line item on the invoice for each component of a kit.  Like this:

Line Item 1: $100 Product A
Line Item 2: $20 Product B (required when Product A is purchased)

Is this possible, or possible with expert customization?

Also, the customer should NOT be able to remove Product B from the cart (unless Product A is also removed from the cart)

Thank you

If you add them as separate products, you will not be able to add the functionality you have requested.

Have you tried using product variants for the “sub-components”? If yes, can you explain why this didn’t work for you? A link to your site will probably add a lot of context for us.

This functionality doesn't exist, so I can't mock up anything for an invoice with two line items that are co-dependent.

The reason I can't use a product variant to represent the combination of Product A and Product B is because... they must be separate line items on the invoice.

I sell Product A on an exchange basis.  When a customer buys Product A from me, they are required to send their old product to me, so that I can rebuild it and sell it to the next customer.  I collect a deposit from the customer at time of original purchase (Product B), and return the deposit 90 days later after I receive their old product.

The same example with actual invoiced line items looks like this:

Line 1: $100 Product A
Line 2: $20 Product B (deposit held until exchanged product is received)
Line 3: $50 Product C (deposit for reusable shipping crate held until exchanged product is received)
Invoice Total Due Today= $170, Customer Payment Received = $170.

90 days later, after the customer returns the shipping crate and their old product...
The refund out of my General Ledger is:
Line 1: -$20 Product B refunded
Line 2: -$50 Product C refunded
Total Credit to Customer = -$70.

Product A is realized revenue
Product B is deferred revenue
Product C is deferred revenue

Our business has been running for 5 years, so I'm trying to avoid changing the bookkeeping processes.

Thank you