Problem

1. Can’t Order Omniplant Seeds on the Mailbox
2. Can’t feed Omniplant
3. Omniplant stopped growing
4. Stuck Omniplants in Inventory

Cause

1. Unclear. Might have something to do with the quality of the seeds not being set properly.
2. Caused by too much stuff in your inventory. If you have a lot of harvestables the selection window fails.
3. If you feed any of the Supernatural fish to the plant (fairy damsel, toad, salamander) the plant fails to produce them (probably because they are missing from the list of available produces) and destroys the plant.
4. The attractions system gives out gifts and one of those is an omni plant. Unfortunately the plant gets stuck in the inventory with no way of using it.

Solution

1. When you get the chance to order them, cancel the interaction while they are on the way to do it. The Seeds should then be ordered from where ever the sim is standing and you will get your seeds the next day
2. Try getting rid of some of your harvestables or use another Sim with less stuff in his inventory to feed the plant.
3. Dispose of the plant and plant a new one. Don’t feed fish from the Supernatural EP to it.
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Mods that help with the issue

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4. Use DebugEnabler to move the plant to your family inventory.