I am no expert in these things, but I believe what you’re describing means that the prv/eth liquidity pool has become unbalanced. It likely means that there was low liquidity in the pool and most of the transactions using the pool have been to buy eth causing there to be less eth available and more prv. I believe the only way to “fix” the pool would be for people to sell enough eth into that pool to better even the sides out.
…Or for ALL eth/prv pool providers to remove their liquidity and create a new even pool.
Now I’m going to go even further out of my depth, but… Before incognito switched to an AMM method, low liquidity pools sometimes meant people got “destroyed” (lost a lot of $) in bad trades because they weren’t paying attention to the trade rates (bad example: paid $15,000 for 1 ETH). AMM “helped” with that making the trade rates “safer” but as a result seems we’ve had horribly unbalanced liquidity pools that mere mortals have no way of fixing and means we cannot contribute to them. Before AMM, when the pools were unbalanced, it was easy to fix (for example if there was very little eth in the eth/prv pool, you would be *incentivized" to sell eth - you would get more $ than it was currently trading for elsewhere).
I wish I could give you a better response and I wish there was a good way for the “broken” pools to be re-balanced… You’re not the only one who would like to contribute liquidity for certain pairs, but found it “impossible.”