Check out the pictures:
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Find "Shop" at the top, hit the triangle, then choose "Bank". That will take you here:
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Interest collection is manual and must be done each day. If you miss a day, or even a month or more, you will still only collect one day of interest when you come back to collect, and your collection time will change to the time of day you come back, with the next collection set for 24 hours later.
NEVER make your deposit or take a withdrawal before you collect your interest or everything resets. The system is a dumb system, not a smart or dynamic system, and will cheat you out of your interest if you touch it for any reason before you collect interest.