The state of Delaware is going to charge your LLC an annual $250 business tax, which would be due every June 1st. You may also be liable to income taxes between the two countries of business and residence. I would definitely suggest consulting with an accountant who is familiar with international taxation treaties to find what other taxes you may have to pay.
You typically require a company bank account to register with a merchant service to accept payments from your U.S. clients. As Italy is a signatory of the Hague Convention, you could get an Apostille with a certified copy of the Articles of Organization. This will allow your U.S. registered business to be recognized in Italy, and you should be able to open your company bank account there. Cayman Islands are signatories to the Hague Convention as well, so you can open a bank account there as well.
(a) You made a typo in the card number, CCV code, expiration date, name or address;
(b) Your card balance is too low;
(c) Issuing bank has declined this transaction for some other reason related to your account.