I've written an algorithm using SetBrokerageModel(BrokerageName.Alpaca, AccountType.Cash); It runs every market open and uses MACD to decide whether to be in SPY or TLT.   I use SetHoldings(...) to accomplish this setting one to 0 and the other to less than 1.0 (I've tried various values).  However,  when it runs, I routinely get "Insufficient buying power to complete order" for a period of 4 days, then the order is filled.  I'm assuming this means the model requires 4 days after a sell for funds to settle before the cash is available for buy?  But reading the Alpaca docs, I dont' see where this is the case.  My understanding is that the results of a sell should be available as "buying power" immediately after it is filled.  What am I missing here?  Algorithm below...

https://www.quantconnect.com/terminal/processCache?request=embedded_backtest_fef4081514e053a7fbca784a4133dcc0.html