Congratulations on your first sale.
Could I suggest that if you want your company to continue to survive and have more sales you employ a professional courier company, expert at international customs clearance and be guided by their rules.
The standard, legal, honest and painfully obvious thing to do is to have accurate documentation attached to the outside of the package and you issue your customer with the standard disclaimer, something like "invoice total includes value of goods and shipping costs, any and all import taxes, duties etc. levied at point of entry to destination are the responsibility of the recipient".
Under-declaring the value of goods on a package transported internationally is commonly called smuggling