In Bolívar – American Liberator, Marie Arana writes about the Congress of Panama:
The conference was to take place on June 22, 1826, on the Isthmus of Panama […]. Bolívar had decided not to attend the proceedings so that it couldn’t be said that he had influenced its outcome. But it was precisely to influence the outcome that the Peruvian delegation arrived six months early, hoping to lay the groundwork for its point of view. As deliberations opened, the nations represented were Peru, Greater Colombia (which now consisted of Venezuela, Panama, Ecuador and New Granada), Mexico and the Federal Republic of Central America; that is to say, only four of the seven Latin American republics. The Argentines had declined outright, saying that they had “a horror of too early a union,” especially one advanced so unilaterally by Colombia. Chile had been too wrenched by internal conflagrations to participate; Bolivia had been willing, but its delegates arrived too late. The kingdom of Brazil, a monarchy with far stronger sympathies for Europe, had also refused, using its war with Argentina as an excuse.
Bolivia was not the only country to miss their flights to Panama.
The United States […] sent two delegates, but one died on the way, the second reached the meeting hall only after the congress was over.
Because the “Treaty of Union, League and perpetual Confederation” was ultimately only ratified by Greater Colombia, rendering Bolívar’s idea of a unified Latin America dead before it could get off the ground, Bolivia’s absence probably didn’t make much difference. But it’s interesting how such coincidences can shape politics and economics: Because Great Britain was present with observer status and the United States were not, Britain secured several trade deals with Latin American countries.