Automating creation of QBO Invoice from data in an Google Sheet... Anybody else doing this?

My target invoices will only have 1 Line Item.

So,  I am starting with a list of invoices I need to create every month and trying to create invoices in QBO.

My chain of zaps is in sequence

1. Google Sheets Trigger (new row)
2. Formatter (to generate Line Items) - only 1 line item really
3. QBO zap - Find Customer
4. QBO zap - Find Product
5. QBO zap - Create Invoice

I have several problems in Step 5

1. In the header section (not Line Items),  setting up the Customer found in Step 3 (Custom tab) does not work.   Test says Customer is not set and fails since its required.   If I hardwire it to something QBO finds through the dropdown,  then Customer setting is remembered (this does not really satisfy my requirements at all, but just something I tried for debugging)
2. In the Line Item section,  I have tried setting up the fields on Price (from Product found in Step 4) and Quantity from Google Sheet & Formatter (Step 1&2) and then setting up Amount to be an expression on above Price times Quantity.  It sometime craps out saying Amount is not set or sometimes it craps out saying Amount is not calculated right.
3. If I hardwire everything as a test,  it fails with some cryptic Business Validation Error.

I assume my requirement for an automated QBO Invoice Creation is not all that uncommon.   Can you comment on whether you are doing this successfully.  Would of course love any tips… I’ve now spent a day hacking around with this and I’m stuck

What is wierd is that I got a similar automation to set up Bills (like my Invoicesm, my bill has only single Line Item) working correctly almost the first time with this flow

1. Google Sheets Trigger (new row)
2. QBO zap - Find Customer
3. QBO zap - Find Product
4. QBO zap - Find Vendor
5. QBO zap - Create Bill
6. Note:  This flow does not even have the formatter for creating Line Items

So,  why is creating an Invoice so problematic when creating a Bill works as I’d expect?

In both cases, I do need to start with the data in a Google Sheet (1 row per target invoice or bill)

I’ve been using Zapier for several years and consider myself pretty knowledgeable on Zapier.  This is however the first time using the QBO Intuit Zap (and the Line Item concept) and that’s where I am running into problems