Your Sable secured credit card has a billing cycle from the 1st to end of every month. You will only need to pay off whatever your statement (that you receive via email in the first 2 weeks of the month) says that you need to pay.
The way this works is as follows: For example if you made $100 of purchases between May 1st and May 31st, you will receive your statement within the first 2 weeks of June and your due date will be June 27th. Any purchases made in June will only be due in July 27th. This is what will be highlighted in your statement that is sent via email.
The due date counter that you see in the app currently only counts down to the 27th of every month as that is the due date for all secured credit cards with Sable currently. Similarly, the balance due shows the current outstanding balance on your Sable account and does not reflect what you may actually owe on your cards. Please follow your statements for accurate information on the amount due and the due date information.