KYC Testing

Meld generally recommends testing the unified KYC flow in production, for a realistic experience.

However if you would like to test the flow end to end Meld's sandbox, first ensure the following is complete.

Make sure your IP address is whitelisted with Mercuryo for their sandbox. If not, you will not be able to load Mercuryo's sandbox. Generally Meld recommends having a static IP address representing your team that you share with Mercuryo.
Make sure the Mercuryo account you are using is set up for Sumsub token sharing, as documented here.
Use a Sumsub sandbox template for doing KYC in Sumsub's sandbox.
Make sure you see both Sumsub and Mercuryo enabled in your Meld dashboard. Reach out to Meld if this is not the case.
After you KYC a user and launch a Mercuryo widget, Mercuryo has to manually approve the user before you can attempt launching the widget again and skip KYC. This constraint is the primary reason to test in production, where this step is not needed.

If all the above conditions are met, you are ready to test end to end! When testing in sandbox you can submit fake KYC data, besides liveness, which must be real.