Sponsor slot management for newsletter operators

The idea

A newsletter doing $3,000 a month in direct-sold sponsorships runs the whole operation on a spreadsheet and an inbox: who booked which date, whether they paid, and whether the creative arrived. The failure mode is always the same: it is Sunday night, the issue goes out at 6am, and the sponsor never sent the image. The operator either scrambles, runs a house ad, or refunds the slot.

Sponsor marketplaces like Paved and Swapstack take 20 to 30% of every deal, which is absurd for operators who source their own sponsors. Pure software for direct-sold inventory, with the sponsor-facing asset portal and automatic deadline nags as the core mechanics, is the wedge. It is a coordination problem, not a marketplace problem.

Who pays

The newsletter operator pays $29/month, and the target is anyone with 10,000-plus subscribers selling slots directly, where a single slot is worth $150 to $2,000. Against a marketplace’s 25% cut on even one $500 slot, the price is invisible. Distribution runs through newsletter-operator communities (Growth In Reverse readers, newsletter Slack and Discord groups) and content on how to leave marketplaces and sell direct.

MVP scope

• Slot inventory with per-type pricing and a calendar of issues showing availability
• Booking creation that auto-generates a Stripe invoice
• Tokenised sponsor portal for asset upload with per-slot-type checklists
• Automatic Postmark deadline nags and an at-risk dashboard
• Skip for v1: sponsor discovery, performance/click reporting, ESP integrations, contracts and e-signature, team seats

Build SlotBook, a sponsor pipeline tool for newsletter operators who sell ads directly. Stack: Next.js (App Router), Supabase (Postgres, auth, storage), Stripe for invoicing, Postmark for transactional email.

Core flow: the operator defines their ad inventory as slot types (main sponsor, classified, secondary) with prices, then sees a calendar of upcoming issues with slot availability. When a sponsor books, the operator creates the booking, which triggers a Stripe invoice automatically and emails the sponsor a tokenised portal link (no login). In the portal the sponsor sees their booked dates, uploads creative assets (image, copy, URL, UTM parameters), and sees the creative deadline. Postmark sends automatic nags at 7, 3, and 1 days before the deadline if assets are missing; the operator dashboard flags at-risk slots in amber.

Pages: calendar view of issues and slots, booking detail, sponsor directory with booking history, inventory/pricing settings, the tokenised sponsor portal, billing.

Non-obvious details: mark a booking as unpaid/paid via Stripe webhooks and block asset go-live status until payment clears; support a per-slot-type asset checklist (e.g. main sponsor needs 600px image, 150-word copy, link) so the portal validates completeness, not just presence.

Pricing: $29/month flat, 14-day trial. One plan; volume-based tiers can wait.