How do I get to continue the Backup of my iPhone 8 Plus?

My iPhone 8 Plus has partially backed up to iCloud Backup. I am trying to continue the backup today, but the message informs me says,

“the last backup could not be completed. iCloud Backup will occur later when connected to power, locked and connected to Wi-Fi.”

I checked on all the connections and all is set and in place. It should continue the Backup, but keeps on repeating same message.

All is Checked OK: the battery 90% & charging to 100%. Power OK.

Screen locked - “Never”.

Wi-Fi OK.

Repeats same message. Please help.