Embed can be configured to use multiple merchant accounts either using an admin API key or a merchant API key.

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Set the merchant ID

Embed can be configured to explicitly take the merchant account ID to process a transaction for. 

<Gr4vyEmbed
  gr4vyId='example'
  environment='sandbox'
  merchantAccountId='my-merchant-account-id'
  ...
/>
Although it’s recommended to set the merchant ID, the ID will fall back to default if not set, which is the standard ID for the single merchant account in a single merchant environment.

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Pinning metadata

When using an API key that has access to multiple merchant accounts (an admin API key) it is recommended to pin the merchant_account_id value when generating an Embed token. 
const token = await client.getEmbedToken({
  amount: 1299,
  currency: 'AUD',
  merchant_account_id: 'my-merchant-account-id'
})
Pinning is not required with merchant API keys as they are restricted to one single merchant account.