An internal transaction is any interaction that a contract does with a specific address (or any internal call within a contract). We listen to the interactions you've set up in your Stream. So if your Stream was set up as a "Wallet Transfer" then there are a couple of points to mention:
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1. We only provide internal transactions where there is a transfer of value.

2. We only provide the internal transactions that mention the addresses you're watching.
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You can monitor internal transactions happening on chain for your Stream by setting the includeInternalTxs parameter to true.