Reminders driving me crazy!

As per the article https://support.apple.com/en-in/guide/reminders/remndbeda47c/7.0/mac/10.15

Mark reminders as complete

In the Reminders app  on your Mac, do any of the following:

• From a notification: Click Complete in a reminder notification when it appears in the top-right corner of your screen.
• One reminder: Select the circle  next to the reminder’s name.
• Multiple reminders: Select the reminders, then select the circle  next to one of the reminders (or tap  in the Touch Bar).

If a reminder is set to have repeated notifications and you mark it as complete, the reminder for that day moves to the completed section of the list. The reminder for the next repeat date appears in the reminders list.

Read this article also https://support.apple.com/en-in/guide/icloud/mmc0cd794a/icloud

You can create and manage to-do items and organise them into lists using Reminders on iCloud.com. You can also share reminder lists with other iCloud users.

Changes you make to reminders and reminder lists on iCloud.com automatically appear on your iPhone, iPad, iPod touch and Mac when those devices have iCloud Reminders turned on.

sandropietro wrote:

When I add a reminder it syncs between Macbook and iPhone but when I update or mark as completed it doesn't update on either device.

So I set it on my iPhone and later in the day mark it as completed. Go and turn on my MacBook several days later and it pops up on screen and stays there.

Or if I set one on my iPhone and then it pops up on the MacBook as I am working I say remind me this afternoon. It changes on the MacBook but not on the iPhone.

Running latest OS on both and have tried anything I can find online.

You do not say what exact Mac /model /year /size /retina /TouchBar is this

or

what exact macOS you are currently running?

and

what exact iPhone or what iOS you are currently running ?

Very your software is up to date on both devices—

The trouble shooting is sign out of iCloud on both devices and sign back in again to jump start the sync.

Sign out of iCloud on your iPhone,...or Mac

sandropietro wrote:

iPhone 11, Macbook Retina 13 inch Early 2015

The exact OS and iOS are the latest as I have said but for clarity:

On the Mac: Catalina 10.15

On the iPhone 11: iOS 13.4.1

It's not sync necessarily that is the issue. It does sync initially, it's when I mark it as completed it doesn't then transfer across.

If it is not transferring across then it is not synching .

The trouble shooting is sign out of iCloud on both devices and sign back in again to jump start the sync.

Sign out of iCloud on your iPhone,...or Mac

sandropietro wrote:

It sync's between them when I create it. On either device.

It doesn't sync when I change it on one device.

I have signed in and out of iCloud on both devices.

For further help with your issue—

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or on line https://getsupport.apple.com/