Default Magneto2 Minimum Order Amount should work fine

go to admin >> store >> configuration >> Sales >> Minimum order amount >> Yes and enter Minimum amount 50.

Check Below attached screenshots.

[![enter image description here][1]][1]

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/ehyLI.png
  [2]: https://i.sstatic.net/LX8EL.png