You don’t need Plus or an app for what you just described. Draft orders do Net 30 natively on every plan, and it maps almost exactly onto the workflow you already have.
Since you’re keying in the orders he emails you anyway: create it as a draft order, then instead of collecting payment choose to send an invoice with payment due later and set the terms (Net 30, or a fixed due date). Shopify emails him the invoice, the order sits as payment pending with the due date attached, and you mark it paid when the cheque or EFT lands. Inventory and fulfilment behave normally. That’s the whole mechanic — no app, no upgrade.
The honest limitation: it’s manual and it’s you doing it. If what you eventually want is your dealer portal offering terms at checkout to approved accounts with no involvement from you, that’s where Shopify B2B on Plus or a wholesale app genuinely earns its money. But for one big account you’re already hand-entering, draft orders will carry you a long way.
The part I’d spend more thought on is the risk side, because the mechanics are the easy half. I’m on the supply side and extend terms to commercial accounts, so from experience:
Run a credit application before you grant terms, even to an impressive name. Two or three trade references you actually phone, plus their AP contact. Large and creditworthy are not the same thing, and the size of the logo tells you nothing about how they pay.
Set a credit limit and start it lower than you’re comfortable with. It’s easy to raise after two clean payment cycles and very awkward to cut after you’re already exposed.
Get the PO number and the exact AP email address up front, and put the PO number on the invoice. This is the single biggest determinant of whether Net 30 behaves like 30 days or 75. Big companies don’t pay quickly because they like you, they pay when an invoice matches a PO cleanly in their system. An invoice missing a PO number goes into a queue that someone has to resolve by hand, and that queue is where your cash flow goes to die.
Put your terms in writing on the invoice itself, including late interest, even if you never intend to charge it. It changes the conversation at day 50.
And model your cash flow at about 45 days even on Net 30. Very few large accounts actually pay at 30, and the ones that pay at 60 aren’t trying to hurt you, that’s just their cycle. Knowing that ahead of time is the difference between terms being a growth tool and terms being a cash squeeze right when you’re scaling up to serve the account.
Congrats on landing it, by the way. Being asked for terms is a good problem to have.