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First of all please make sure you have selected post type while creating custom fields. Then please follow below explained few steps.
1 – If you are using gutenberg (Block) editor then please sure your settings are enabled to show extra areas in editor, This is wordpres default setting. Please see screenshot and follow the instruction to verify your editor settings.
2- If you are using classic editor then please find “Screen options” at right top corner and click on it, You will see your already created custom field’s groups are there, make sure all groups are checked.
If problem is still there please write us again we will be back to you.