Disappointed with RobinHood: found out my CSP is costing me interest.

My August interest payment seamed really low, given 4% for RH Gold.

Did some digging and $7500 ($75 strike * 100) of my cash was sequestered to cover a CSP I wrote. Leaving almost no cash to accrue interest.

($7500*0.04)/12 = $25/month in forgone interest. I'm only maxing about $200 on the CSP assuming it expires but the contract is costing me over $50 in forgone interest.

Maybe not news to others, but Fidelity doesn't do this. Guess I'll avoid trading CSPs in my RH account going forward.

Follow on Question: If my cash balance was $0. Would a sold to open Put be charged margin interest, or would I get a free ride?