Using HELOC on fully owned rental as down payment for next rental

I would like to use a HELOC on a rental property that I have fully paid off to pay for my next rental. My concern is using that credit to pay the down payment for the mortgage. Everything I have researched so far has strongly advised against this, and suggested only using the HELOC to purchase a property in full. The only difference is in all of these examples I have researched, they take out a HELOC on a property with its own mortgage. My property has none.

Is this a good idea? Has anybody else executed a similar plan? Any other advice? Thanks!