URGENT: Windows stopping me using Serif Photo Pkus SE with time running out!

I have very little time left and am trying to hold up a publisher!

Serif Photo Plus SE.

Windows has blocked this software because it cannot verify the publisher.​

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There is no way whatsoever I can over-ride this trespass by Windows.
I used Serif Photo Plus SE successfully 3 days ago and it is an established brand software.
Microsoft's negligence is going to lose me money tonight.

Can someone please help me .......urgently, extremely urgently?

Thank you, Jon

 

To late, lost the order.