Their representative recommended I engage with JP Morgan Chase private banking / wealth advisor as they thought this would allow them to be more creative and include other assets as part of the collateral.

Quote from @Kevin Akers: If you have everything else in place (financing, permits, etc) and have underwritten the deal where the numbers make sense you can work on raising the 50K from private investors. 

Investing as a limited partner/ passive investor is a somewhat risky endeavor whether it in private placement or in the public markets.  

You could pay them a flat interest rate on the funds they contribute, similar to a private lender, or offer a percentage of the profits to align their success with yours.

Hard Money Loans: These are short-term loans from private lenders based on the property's value rather than your credit score.

Strictly from a private money lens: If you're open to a 2nd position private money loan against your STR's, it's possible.

I’m still working the in’s and out’s of BP but I will try and send you a private message. 

I know I can reach out to some mortgage brokers to connect me with a private lender for most of the mortgage and then I would just need another lender to supply the down payment and renovation money.

I should note that that I was using Baselane's banking service to collect deposit and rent, and had moved the funds immediately to my private bank after I collected (thank god!).

If it's private money, they would issue a letter.