Hello,

We do have some documentation regarding the pricelist management in POS

https://www.odoo.com/documentation/17.0/applications/sales/point_of_sale/pricing/pricelists.html#:~:text=Select%20pricelists,-Go%20to%20the&text=When%20you%20open%20a%20POS,desired%20pricelist%20from%20the%20list.&text=Multiple%20pricelists%20must%20be%20selected,price%20will%20not%20be%20adjusted.

So if you want to have the price changed in POS when you put 50 units, check the following configurations to be set 

- Manage minimum quantity to activate the rule

- Select or remove the country group if you want it to apply to specific locations

- Set your configurations to enable the pricelist by default or if there many pricelist set them up directly

if you check these setups then the POS session will be able to select the pricelist in the UI section 

Be sure to test it out in a normal sales order if you wish to make any quick configurations or adjustments

The configurations are available for v17