You have to edit both careerSavegame.xml and farms.xml, and ensure that the money matches in both files. farms.xml will have a number followed by a period and several 0's. Just change everything to the left of the decimal to match what you've changed in the career file.

First go to your savegame, for example first save slot:

documents / mygames / FarmingSimulator19 / savegame1 / careerSavegame.xml

and change this line near the end

[money]500000[/money]

Then go to;

documents / mygames / FarmingSimulator19 / savegame1 / farms.xml

and change this line near the end

money="500000?

to whatever you like - have fun!