Unable to remove Add-on (See explanation in Body)!

[Paul]

I realise that this is related to an add-on, however since the develiper isnt responding at all i have no-where else to turn....

This is with regards to the "[XTR] Custom post fields" addon which has been deleted.
I have tried to contact the add-on's support via their online ticketing on this since I'm actually unable to uninstall this add-on, but no response, so i'm reaching out to see if anyone (who has more experience than me) could advise please?

When i try to uninstall, i get...

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Unable to remove Add-on (See explanation in Body)!

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