Hi Giovanni,
You are mentioning the T code is ABZON, but the account key VS4 pertains to sales tax.
The accounting entry at ABZON will be
Asset DR
Contra Account CR(Which is configured in AO90).
So ideally no sales tax GL is involved.
So check the Contra GL account assigned in AO90.
Study the root cause at your end and revert back with the findings.
If still the problem persists attach screenshot of ABZON and AO90.
Hope it solves.
Regards,
G.Sethuraman