SQL Backup job failed with exitcode: 880 SQL error code: 942 [SQLSTATE 42000] (Error 50000). The step failed.

When a database is offline and you try to take backup of that database than below error will show:

SQL Backup job failed with exitcode: 880 SQL error code: 942 [SQLSTATE 42000] (Error 50000). The step failed.

So, before running backup on any database, check whether the database is online.
Now to make database online, you can use below methods:

Method 1

use master
go
Alter Database <Database_Name> SET Online

Method 2

Open SSMS, select database, right click. Select Tasks and Select Bring Online.