Clarifying a BRRRR point - BUY must be done with 100% cash?

[Billy Seol]

Hello! I've been reading up on the BP core books. I read "Investing in real estate with no and low money down" first, and then am reading BRRRR now. I thought I understood the process after reading the first book but after reading BRRRR I feel like I need to clarify my understanding.

I have a primary residence home right now, that I got a HELOC out of. I was going to:
1. Find an investment property to purchase
2. Use the heloc as a down payment (10~20%)
3. Finance the rest from a lender
4. Rehab (using heloc)
5. Rent
6. Refinance after the forced appreciation on the investment property, and use that money for the next purchase & pay off the initial down payment from Step 2

However, the BRRRR book said I needed to make the purchase with cash. Is it essential that I use cash for the initial purchase? Or is it that I need to use the HELOC completely to purchase the property, basically put 100% down with the HELOC & the rehab? As this is my first purchase I'd like to make sure that I put the "first button on the shirt correctly", so to speak. :)