How I can upgrade health point for the player?

For increase player health point you need get the gold cards, gold cards you an get in the battles or buy in the Shop.
Gold cards you can get to wins in thre Versus Mode or Story Mode.

Can I play with another player on the one PC?

Yes, you can play with another player on the one PC: Go to Versus Mode -> Player vs Player.

Can i play on the game used cross-platform online mode?

Yes, you can get the game on Android/iOS/PC and play with another players online mode used.

What in-app and in-game purchases are offered in your product?

Player can get gold cards for winner place in the battle or he can get them for In-App Purchase in the game shop, for gold cards player can increase default health for character.

Example in-app purchases include the following:

+100 Gold
+500 Gold
+1000 Gold

Does the product use Epic Games' payment platform or your own for these in-app purchases? Note: Epic can not provide details or refund for any transactions made outside of Epic's payment platform.

When playing "The Lost On The Street" through the Epic Game Store, all in-app purchases use Epic Games’ payment platform. The in-game store transitions the user to the platform storefront to complete purchases. When playing on other platforms, different payment platforms may be used.

Can I use your product without making any in-app purchases?

"The Lost On The Street" does not require players to purchase any content to play. All purchases are optional and provide only some skills benefits. Virtual currency player can get via win in the battles as well.

Are the in-app purchases refundable?

In-app purchases made on the Epic Games payment platform are eligible for refund within 14 days of purchase if they are marked as “refundable” or “self-refundable”.