## Summary
- When a transaction ID is provided during sync, check if it already
exists before creating
- If it exists, return the existing transaction with 200 status instead
of failing with duplicate key error
- Prevents duplicate transactions when sync retries occur due to network
issues
## Test plan
- [x] Attempt to create a transaction with a specific ID
- [x] Attempt to create another transaction with the same ID
- [x] Verify the second request returns the existing transaction instead
of an error
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