Key Takeaways

• Most supply chain verification issues start at onboarding. The SSP is live and serving ads before ads.txt and sellers.json are verified. Revenue runs at reduced capacity from day one.
• The checklist has three phases: pre-launch, launch day, and post-launch. Each phase catches different issues.
• sellers.json verification is the most commonly skipped step. Publishers add the ads.txt entry and assume the SSP handles sellers.json. Often, they don't.
• The full checklist takes 15-20 minutes per SSP. A small investment that prevents weeks of lost revenue.
• Reuse this checklist every time you add an SSP. Consistency prevents the ad hoc mistakes that create verification gaps.

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ads.txt Checklist Before Going Live With a New SSP

When you onboard a new SSP, there's a standard process: sign the contract, configure the ad server, add the SSP to your header bidding wrapper, test the integration, and go live.

ads.txt and supply chain verification are often afterthoughts, handled after the SSP is already serving.

That delay costs money. From the moment the SSP goes live until ads.txt and sellers.json are properly configured, DSPs see unverified supply through that SSP. Premium demand is either absent or discounted.

Use this checklist every time you add a new SSP to ensure verification is in place from day one.

Phase 1: Pre-Launch (Before the SSP Goes Live)

Gather SSP Information

Before adding anything to ads.txt, collect from your new SSP:

• [ ] Exchange domain. The exact domain to use in ads.txt (e.g., openx.com, pubmatic.com). Ask the SSP if unsure. Some SSPs use a different domain for ads.txt than their main website.
• [ ] Account ID. Your specific seller_id on their platform. This must exactly match what they'll use in sellers.json and bid requests.
• [ ] Relationship type. DIRECT if you have a direct contract and payment relationship. RESELLER if an intermediary is involved.
• [ ] TAG-ID. If the SSP is TAG-certified, get their TAG-ID to include as the fourth field.
• [ ] Reseller requirements. Does the SSP work with other exchanges that also need RESELLER entries in your ads.txt? Get the full list.

Verify SSP Has sellers.json

Before going live:

• [ ] Check that the SSP maintains sellers.json. Navigate to https://ssp-domain.com/sellers.json. Confirm the file exists and loads.
• [ ] Ask when your entry will appear. Some SSPs add entries automatically when you onboard. Others require a manual step. Confirm the timeline.
• [ ] Request non-confidential status. Explicitly request that your entry be marked non-confidential. Some SSPs default to confidential for new accounts.

Prepare the ads.txt Entry

• [ ] Format the entry correctly. exchange-domain.com, account-id, DIRECT, tag-id with proper comma separation.
• [ ] Include reseller entries. If the SSP requires reseller entries for their exchange partners, prepare those lines too.
• [ ] Test the format. Run the new entry through an ads.txt validator to catch formatting issues before deployment.

Phase 2: Launch Day

Deploy ads.txt Update

• [ ] Add the new entry (and reseller entries) to ads.txt. Deploy the updated file to your live domain.
• [ ] Verify the file is accessible. Navigate to https://your-domain.com/ads.txt and confirm the new entry appears correctly.
• [ ] Check formatting in context. Make sure the new entry didn't introduce formatting issues (missing newlines, encoding problems) that affect other entries.

Activate the SSP Integration

• [ ] Go live with the SSP in your ad server. The SSP should start receiving ad requests.
• [ ] Confirm ad requests are flowing. Check the SSP dashboard to verify impressions are being received.

Initial Verification

• [ ] Check sellers.json. Navigate to https://ssp-domain.com/sellers.json and search for your account ID. Confirm your entry is present.
• [ ] Verify entry details. Check that name, domain, seller_type, and is_confidential are correct.
• [ ] Cross-verify. Confirm the account ID in your ads.txt exactly matches the seller_id in sellers.json.

If the sellers.json entry isn't yet present, note the expected timeline from your SSP and schedule a follow-up check.

Phase 3: Post-Launch (First Two Weeks)

Week 1 Checks

• [ ] Re-check sellers.json. If the entry wasn't present at launch, check again. Contact the SSP if it's still missing after five business days.
• [ ] Monitor CPMs. Check the new SSP's CPM performance against your expectations and other SSPs. Unusually low CPMs may indicate verification issues.
• [ ] Check for errors. Review the SSP dashboard for any error messages, timeout issues, or bid rejections.
• [ ] Verify schain. If possible, confirm the SSP is propagating complete SupplyChain objects in bid requests.

Week 2 Checks

• [ ] sellers.json final verification. Your entry should be fully live by now. Run a full cross-verification using BeamFlow's scanner.
• [ ] Performance baseline. Establish a CPM and fill rate baseline for the new SSP. This becomes your reference for future monitoring.
• [ ] Compare against existing SSPs. Is the new SSP's CPM competitive with your other SSP partners? If way lower, investigate whether a verification issue is the cause.
• [ ] Update your tracking. Add the new SSP to your monitoring system, audit spreadsheet, and any other tracking tools.

For Multi-Domain Publishers

If you manage multiple domains, add these steps:

• [ ] Identify all applicable domains. Determine which of your domains will use the new SSP.
• [ ] Gather per-domain account IDs. If the SSP assigns separate account IDs per domain, collect all of them.
• [ ] Update ads.txt on every applicable domain. Deploy the new entry across all relevant domains simultaneously.
• [ ] Verify sellers.json for every account ID. Each domain's account ID needs its own sellers.json entry.

Common Onboarding Mistakes

Mistake 1: Adding the SSP to the ad server before ads.txt

The SSP starts serving ads and running auctions before DSPs can verify the supply path. Revenue runs at reduced capacity until ads.txt is updated and DSP caches refresh (1-3 days after the update).

Prevention: Add the ads.txt entry before or simultaneously with the SSP integration going live.

Mistake 2: Using the wrong account ID

The account ID in ads.txt doesn't exactly match the seller_id the SSP uses in sellers.json and bid requests. Even small differences (leading zeros, different formatting) cause verification failures.

Prevention: Get the exact account ID from the SSP's onboarding documentation or support team. Copy-paste rather than manual entry to avoid typos.

Mistake 3: Skipping sellers.json verification

The publisher adds the ads.txt entry, sees ads serving, and considers onboarding complete. The sellers.json entry is missing or incorrect, causing silent CPM reduction.

Prevention: Always check sellers.json within one week of go-live. Don't consider onboarding complete until verification passes.

Mistake 4: Forgetting reseller entries

The SSP works with exchange partners that also need RESELLER entries. Without them, bid requests through those paths are unauthorized.

Prevention: Ask every new SSP whether additional RESELLER entries are required for their demand partners.

Quick Reference: The 10-Point Checklist

1. Get exchange domain, account ID, relationship type, and TAG-ID from SSP
2. Verify SSP has sellers.json
3. Request non-confidential status
4. Add formatted entry to ads.txt
5. Add any required reseller entries
6. Deploy updated ads.txt and verify accessibility
7. Go live with SSP integration
8. Check sellers.json for your entry within 24 hours
9. Verify entry details match ads.txt data
10. Full verification at week 2 using BeamFlow

Frequently Asked Questions

How soon should I check sellers.json after going live?

Within 24 hours of the SSP being active. If the entry isn't there, check again at day 3 and day 5. If still missing after five business days, escalate with the SSP.

What if the SSP doesn't have sellers.json?

This should be evaluated before onboarding. An SSP without sellers.json means your inventory through that SSP can't be fully verified by DSPs. Consider whether the demand quality justifies this limitation.

Can I add the ads.txt entry before the SSP is configured?

Yes. Adding an ads.txt entry for an SSP that isn't yet serving your inventory causes no harm. The entry is ready for DSPs to cache, so when the SSP does go live, verification is immediately available.