This is not the right forum for your question. It is for SAP Business One user only.
Please close your thread and post it on a proper forum such as here:
To appear the TAX codes in FB70 dropdown list you need to assign those new tax codes in the below configuration.
Spro -> financial accounting -> Accounts Receivable and Accounts Payable ->Business Transactions-> Outgoing Invoices/Credit Memos->Outgoing Invoices/Credit Memos - Enjoy ->Define Tax Code per Transaction
in that selct your country and in the next screen select new entries button and add those new tax codes. when adding chose the option FIAR FInancial accounting out going invoices. and save the entries.
after this setting you can able to see those new tax codes in FB70 dropdown list.
hope this helpful.