The notion of surplus value isn't real, it's an arbitrarily made-up idea without an essence (see Aristotle.)
All that matters is this: I ask you to mow my lawn and you say sure, if I pay you $20. We both agree. You mow my lawn and I give you $20. That's it.
Every human being values everything differently. If someone else came along and for reasons that are their own decided to give me $1,000 because they loved my lawn so much and I agreed to accept that, the two of us made a transaction. We, as consenting adults, made an agreement. It has nothing to do with you. You do not get to come along and tell me we cannot make that trade, that it isn't worth $1,000, or that I now owe you $500 because you were the one who mowed it.
In fact, the $1,000 itself has no intrinsic value. The value of a given currency fluctuates by the minute. Something on a store shelf could be selling for $1 today and $2 tomorrow, then $0.50 Wed and $5 by next week Friday. Then something else could be worth completely different values too.
Maybe this week $10 gets me a meal and a t-shirt but tomorrow it gets me 2 meals and a t-shirt and the following week I can't buy any meals or t-shirts at all - with that same $10.
EVEN if it were some kind of objective concept, what exactly would the numbers be in a network where everything has value independent of everything else?
Let's say you work for me and make shirts. I pay you $10 a shirt and sell it for $20. You might say that according to Marx, I should give you $20, and let's leave out everything else for the sake of argument. Why is $20 the value?
What if I also own the grocery stores, and I agree to pay you 100% more and raise the grocery prices by 100%? So now instead of you having $10 and a loaf of bread costing $1, I now give you $20 and that loaf of bread now costs you $2? So you now have the exact same buying power and I'm now making the same value from you.
No offense if you are a self-proclaimed Marxist, but I find that the socialist/communist crowd rarely thinks through their positions.