This is the 1895 2c postage due with the Postage Due overprint reading downwards. It is only available with a CTO bar cancellation. The most expensive variation would have the overprint reading upwards omitted in pair with a normal.
This 12c crocodile adhesive has the double overprint but unfortunately has some tone spots. Almost all the stamps in this issue have the double overprint variety. They are only available as CTO which is not surprising. You can draw your own conclusions.
I posted this a few years back but it is a good idea to put these errors on the same page. This shows the horizontal and inverted overprints for the 1895 18c postage due stamp.
This 1902 18c postage due has the double overprint which is available mint or CTO.
I posted this a few weeks ago and I think this 1901-02 3c postage due with stop has the double overprint variety having bought it at the normal price.
I posted this a few years back but it is a good idea to put these errors on the same page. This shows the horizontal and inverted overprints for the 1895 18c postage due stamp.
This 1902 18c postage due has the double overprint which is available mint or CTO.
I posted this a few weeks ago and I think this 1901-02 3c postage due with stop has the double overprint variety having bought it at the normal price.