Duplicate lesson ID: course-42 (subject 'Mathematics', group '5A'). Lesson IDs must be unique.
Last updated: Mar 23, 2026
At a glance
Two lessons share the same internal ID.
What causes this error
Every lesson must have a unique internal identifier. This error typically occurs when importing lesson data from an external source (e.g. Excel) where the same ID was assigned to multiple lessons.
How to fix it
If importing from Excel, check the source file for duplicate IDs and correct them before re-importing. If the data was entered manually, contact support.
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