The correct output VAT amount to submit on the VAT Return for July should be THB 405,193.25 and the amount payable to the Rev Dept should be THB387,848.26.
It would be preferred to have the July VAT return and reports revised to show the correct amount if possible by Wednesday morning Bangkok time.
Sorry, I missed your call as this was after hours and I had already left office for home - I understand the geographic timing differences makes it difficult and always appreciate your help and support.