Backup taking more than 24 hours and then fail

nadinz25,

Thank you for reaching out at Apple Support Communities today. If I understand correctly you haven’t been able to get your iPhone 6s to complete an iCloud backup for a couple of months. It sounds like you have the basics down with it locked and connected to power and Wi-Fi. Let’s see if we can determine why it isn’t completing.

We’ll reference the guidance in this article to start: If you can't back up to iCloud or restore from iCloud backup failed

You mentioned that you were purchasing additional iCloud storage. We can start by comparing your available storage to the size of your backup. 

• Go to Settings > [your name] > iCloud

• What does it say in the top graph for iCloud storage? You should see something like “## MB/GB of ## GB Used.” Then click on Backups > [your iPhone] from that page and check to see what it says for “Next Backup Size.” 

• You can manage what iCloud backs up  by turning off any of the apps you may not need in your backup.

Let me know if these help.

Cheers.