You can only start setting up Notification URL if you have done the Credential Exchange step, otherwise the button will be disabled. Do this for both Sandbox and Production.
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Setting up BI SNAP Notification URL
- Go to Settings > Payments > BI Snap Notification URL
- Fill in your Notification URL endpoint at the 'Set notification URL' section, then click Save.
- Afterwards, the Midtrans Public Key will be generated.