You will need to change automatically apply credit setting OFF.
To do to this:
From the Home page screen
Select the Company Gear (top upper corner)
Select Company Settings under Settings header
Under Automation, change automatically apply credit setting to “off”
Change automatically apply bill payments to “off” as well
See screenshot photo for reference
Not sure how you’ve recorded $900 payment. You may have it try it out like delete/void payment, receive payment again to fix it. Again, I do not see your books from here.