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Offsets are retired in batches and each retired batch of credits has a unique serial number provided by the registry after retirement. For VCS credits, it looks something like this:
0001-000001-000100-VCS-VCU-003-VER-US-0003-01012020-31122020-1
This serial number carries a lot of relevant information, including the number of offsets, certifying standard body, project identifier, country, monitoring period (vintage), and more. The full taxonomy can be found here.
The next step is to update the BatchNFT with this serial number. Now the link between the legacy and on-chain registries is complete—the BatchNFT is linked to the retirement entry in the legacy registry through the serial number and the retirement entry has the NFT's unique identifier in its metadata. These steps are key because they ensure that double counting / double bridging of carbon offsets is not possible.
Furthermore, the serial number is used to update the BatchNFT with project-specific attributes, some of which are stored on-chain while others are stored as metadata on IPFS. This information will be useful down the line. Submitting the serial number to the BatchNFT contract changes the state of the NFT to awaits approval.
We discovered that some retirements (especially those made through EMA) sometimes return multiple serial numbers. You can input these numbers in the interface by clicking + to add additional fields.
These serial numbers must all refer to the same project AND vintage, as described in the Retire section.

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In order to complete the one-to-one link between the source registry and the on-chain, tokenized carbon offsets, we need to write the serial number we received from Verra on chain. This ensures that every Toucan carbon offset can be easily traced back to the entry in the source registry.
  1. 1.
    From the interface we left at the end of the Initialize step, click "I have retired my credits" to advance to the next page.
  2. 2.
    Paste the serial number provided by Verra into the text box. Clicking "Confirm serial number" should trigger the app to fetch project details and display them. Inspect this to make sure it all looks accurate!
  3. 3.
    If it all looks accurate, "Submit for approval", review the data in Metamask and click Submit to sign and broadcast the transaction to the network.
  4. 4.
    Check to make sure that [email protected] was included in the retirement confirmation email you received from Verra. If not, forward that email to [email protected] with the batch NFT token ID in the subject line.
Great! You've completed the first sequence in the bridging process.
Last modified 1mo ago
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