Alpaca said this morning that it has closed a massive $50 million Series B round of capital. TechCrunch previously covered the company’s late-2019 $6 million seed round and its late-2020 $10 million Series A. Alpaca offers equities trading software via API. The company initially allowed firms to plug into its technology, powering the trading capabilities of investing groups. More recently, Alpaca has begun allowing other fintech companies to offer equities trading through its service to their consumer user bases, work that fits under the larger embedded finance trend. Tribe Capital led…