There are three amounts you need to be aware of and understand each balance. You have a minimum due, that must be paid by the last day of each month at 11:59 PM ET.
The other amount is the statement balance, which to avoid interest charges must be paid no later than the last day of the month at 11:59 PM ET. If you pay less than the statement balance, you will pay interest the next two months.
The final amount is the account balance, which is all that is due. Account balance will not reflect pending charges you’ve made recently.
You can make up to 5 electronic payments per day or approximately 150 payments per month. Just make sure you’ve paid a sum equal or greater than the minimum due by the last day of the month.
How to make Apple Card payments - Apple Support