how do i keep apple care on my phone

Follow this guidance→About continuing your AppleCare+ coverage for iPhone, iPad, and Apple Watch - Apple Support. While it isn’t clear in the article, you must wait until the current AppleCare has expired to extend it. To be safe add a reminder to do it the day after it expires.

The_seen wrote:

How do you pay for apple care monthly

ref

AppleCare Products - iPhone