Well, the problematic thing with Andreas Palaiologos' claim to the throne of the Eastern Roman Empire was that he already sold it once, before to Ferdinand II of Aragon; He sold it first to the King of France Charles VIII in 1494. This has been attested to by Étienne Lauréault de Foncemagne in his letters.

However, it is a moot point on whether Charles VIII or Ferdinand of Aragon has the real claim; According to Potter, in 1566, Charles IX disdained and let go of the imperial claim to the throne of the Eastern Roman Empire partly due to the principle of Extinctive Prescription (whereby a claim is rendered expired due to prolonged inability to claim the inheritance named) and partly due to his focus on the wars of religion.

As for the claim that Ferdinand II purchased, it can also be considered to have expired under grounds of Extinctive Prescription, though since the Spanish constitution that governs the rights and titles of the King and Crown of Spain does not have provisions for E.P., it is more accurate that it should be labeled as a "dormant claim", though there is (at the point of this writing) any attempts to use the claim since it was purchased.

SOURCES:

• Étienne Lauréault de Foncemagne, Mémoires de literature, tirés des registres de l'Académie royale des inscriptions et belles lettres
• David Potter, A History of France, 1460–1560: The Emergence of a Nation State