In September 1944 the Bulgarian surrender caused a political vacuum in Macedonia, which the Germans filled with a local puppet government. The German postal authorities took over the post in Macedonia. The post continued to use postage stamps of Bulgaria until the overprinted set were available. Macedonia had been occupied by Bulgaria since 1941.
By the time the stamps were issued on the 28th October 1944, more than half of the country had been overrun by the Soviets and partisans. The local government in Macedonia could only rule so long as the Germans remained in the country. The Germans were fighting a withdrawal northwards and the last of the troops left Macedonia on the 13th November 1944.
That is to say the local occupation stamps were on sale, and valid, for only two weeks! of the local people wished to be caught with the stamps when the Soviets marched in and as a result some 98% of those stamps sold were sold to Wehrmacht troops passing through.
An envelope containing a complete set of the overprinted stamps. Very few would have been used in day to day postal use, as they were only valid for two weeks (this cover was probably for a Wehrmacht philatelist passing through Skopje)
28th October 1944 : The set of eight stamps with the Macedonia Overprint
The date on the overprint is not the date of issue, but the date that the local government was set up by the German authorities. The original stamps are Bulgarian, with the word "MACEDONIA" within the overprint.
There are many variations or mistakes within the overprint, for example upside down or a full stop missing etc.