Hi Thai,
Thank you for taking the time to reach out and get this resolved so we can get you back to business. Being able to make payments on invoices is a key part of QuickBooks Online. I'd be happy to point you in the right direction with this.
One of the great features of QuickBooks Online is how it allows you to make payments directly through the payments add on. When a credit card works at first but the next payment is declined I recommend reaching out to the bank as the reason for the decline is through them. As soon as your client speaks to them they should allow the payments through and remove the flags or blocks.
Should you continue to have issues making payments after speaking to the bank I suggest reaching out to our payments department to make sure there is nothing wrong on the account end. You can get in touch with them using the following methods.
Schedule a Callback or start a Chat: click (?)Help in the upper right in QuickBooks Online > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
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Support hours are from Monday to Friday between 9 a.m. and 8 p.m. ET
Have a great day!
