My tax payable a/c doesn’t show the exact value asper posted invoice;
my VAT rate is 18% on posting the invoice and printing it shows a pcorrect amount but when I visit GL the amount is different as seen below
You have not shown enough information to know that these screen shots are related. Please post the entire Edit screen for the sales invoice. Also post a screen shot of the Edit screen for the Standard Rated tax code definition. Finally, do you have more than one currency enabled? If so, post screen shots of the Edit screens for the currencies and the customer involved in this sales invoice.
@RIGO_TZ, @Joe91 is correct. You should not have defined your tax code as you did. It is possible you are operating under a flat rate scheme in your country, but not with a flat rate percentage the same as the tax percentage. There would be no point. Read about flat rate schemes in the Guide @Joe91 linked.