The Greek pressures on Skopje regarding the non-implementation on items agreed upon, are based on Article 8 and more specifically on paragraphs 2 and 3, ie, the designation of the Greekness of the ancient Macedonians and of course the removal of the Sun of Vergina.

Article 8.2
Within six months of this Agreement coming into force, Part Two ought to review the status of monuments, public buildings and infrastructures within its territory, as to whether and how they are in any way referred to the ancient Greek history and civilization that constitute an inextricable aspect of the historical or cultural heritage of Part One, and should take appropriate corrective actions in order to deal effectively with the issue and to ensure all due respect toward the prementioned heritage is given. [p.11 / 20]

Article 8.3
Part Two will never and in no way use the symbol previously depicted upon its former national flag in all its forms.
Within six months of this Agreement coming into force, Part Two should result to the removal of the symbol depicted upon its former national flag from all public places and public uses within its territory.
Archaeological artifacts do not fall within the context of this provision. [p. 11/20]

Additionaly Greece has also stated that it will not accept merely symbolic moves which will take place at the last minute due to the meeting at a European level in October.
In other words, Greece exerts a reasonable pressure upon a neighbour who said that they only saw positively everything they had agreed upon.
Because the six month period after the signing was officially given for the implementation of the measures and especially the provisions of Article 8.
Whereas Skopje is trying to put it across as the initiation of the decisions for future implementations.
In this manner, Greece is forcing Skopje to indicate its true will and not to function merely diplomatically without having any consequences in regards to what they have agreed upon.
We have observed a similar strategic implementation at the time of the negotiations up until we’ve reached the level of the Fifth Annan Plan.
The internal problems of Skopje don’t allow them for much room for a motion, and Greece is aware of it, so that is why it’s applying pressure for the implementations, in order to indirectly prove that the text is in actual fact invalid.