Papertrade advertises zero fees. I went through the numbers on a simple trade and that isn't what I found.
Say you go long Bitcoin at $80,000 with $1,000 of margin at 1000x. Your position is worth $1M, or 12.5 Bitcoin.
Each $1 move in Bitcoin is $12.50 to you. Your $1,000 covers an $80 drop, so your margin runs out at $79,920.
Papertrade liquidates you at about $79,960. That is a $40 drop. At that point you have lost $500 on paper, but they keep the full $1,000.
On the winning side, say Bitcoin goes up $50 to $80,050. Your profit on 12.5 Bitcoin is $625. Papertrade pays you $406, which is 35% less.
Here is what they pay at different move sizes:
A $25 move earns $312 and pays $157. That is a 50% cut.
A $50 move earns $625 and pays $406. That is a 35% cut.
A $100 move earns $1,250 and pays $940. That is a 25% cut.
A $200 move earns $2,500 and pays $2,032. That is a 19% cut.
A $500 move earns $6,250 and pays $5,333. That is a 15% cut.
A $1,000 move earns $12,500 and pays $10,843. That is a 13% cut.
The cut gets smaller as the move gets bigger, but it never goes away.
At 1000x most trades end on small moves, because Bitcoin moves $40 or $50 all the time. Small moves are where the cut is largest.
Putting the two sides together, a $40 drop costs you $1,000 and a $50 rise pays you $406. To break even on those terms you need to be right about 71% of the time.
For comparison, Hyperliquid would charge roughly $900 in taker fees to open and close a $1M position. That fee is stated up front. Your margin also runs all the way to zero before you are liquidated.
On Papertrade the cost comes from the early liquidation and the reduced payouts on wins. Each one shows up in the price you get rather than as a fee. Combined with 1000x leverage, it puts the odds well against the trader.