en.wikipedia.org/wiki/Spain_during_World_War_II

The official record of the Potsdam Conference contradicts this claim.

• In the published Joint Report With Allied Leaders on the Potsdam Conference (August 2, 1945), the section on Spain says only that the three governments would not favor any application by the present Spanish Government for United Nations membership. It does not announce a trade embargo.
• The Foreign Relations of the United States minutes for the July 19, 1945 Potsdam meeting show Churchill arguing against Stalin's proposal to break relations with Franco's Spain. Churchill also said Britain had "valuable trade relations" with Spain and that, unless convinced it would help, he did not want this trade stopped.
• Historian Enrique Moradiellos summarizes the outcome of Potsdam as a "bald rhetorical declaration" with "no effective sanctions, be they diplomatic, economic or military" and calls it a "toothless international ostracism."

So the historical record shows the opposite of what the article says: Potsdam did not produce a "full trade embargo against Spain."

This sentence gives the wrong date for the Japan-Spain agreement.

The official treaty text identifies the agreement as an "Exchange of notes constituting an agreement" between Japan and Spain made in Madrid, 8 January 1957. It also states that it came into force on 8 January 1957. The Japanese Foreign Ministry's treaty database likewise lists the agreement on Spanish claims with an effective date of 1957-01-08.

So while the amount of $5.5 million matches the treaty, the statement that Japan concluded the agreement with Spain "in 1954" is incorrect. The Spain agreement was a 1957 agreement, not a 1954 one.