This might be a Translation Convention for the audience's benefit (if a bit of Viewers Are Morons, frankly), but the series uses repeatedly the name Spain when it should be using Castile.
Contrary to what the series shows, the expedition's crews weren't composed by "people without a job and fugitives from justice" or even convicts recruited directly from prison as shown in the prologue, but professional sailors, many of them very experienced in this kind of travel. Oddly, it seems even the scriptwriters themselves forgot about this point, as one of Elcano's lines at the end is exactly "you all freely chose to come along this travel" (something not even he did in this version, having been recruited in jail).
Also contrary to what the series shows, as well as pop culture (and what Elcano's actor Álvaro Morte claims), no sane, educated person in the 16th century believed the world was flat, as the Earth being a globe had been accepted knowledge for 2,000 years by that point. Elcano's claim that by circumnavigating the globe they will "prove that it is possible to navigate around the world" is nonsense, as it was already considered a feat perfectly doable (if highly difficult and not worth the effort) at the time.
The Giralda of Seville featured in the series has its appearance from 1568, many years after the time the series is set. This is likely a goof, as the same tower is shown in its proper appearance in other scenes.
In the series, Pigafetta reveals he studied indigenous languages to communicate with the Guaraníes. In real life, it was an unrelated crewman who spoke a bit of Guarani, João Lopes Carvalho.
The series has a crewmember from Madeira named Omar. At the time, you could not be a Christian without having a Christian name, not to mention a Muslim name of all things.
The cultures of both Cebu and Mactan are given a weird, misplaced Polynesian flavor, not only having everybody wear loincloths, but also showing Lapulapu doing the Maori tongue taunt and wielding a leoimano. In real life, leaving aside this geographical absurdity, there should have been more of an Indian imagery present, with silk robes, turbans and sabers among them, more similar to how Tidore natives are portrayed in this very series.
Humabon is portrayed as basically a tribal chief, governing over a primitive village on an island, when in real life he was an aristocrat who ruled over a relatively developed Indianized rajanate. The series also excises that Humabon was converted to Catholicism under the name of Carlos.
It's perhaps possible that Magellan and company were the first Europeans whom Humabon personally met, but it's unfathomable that he could have ignored the value of clove in sea commerce around the Philippines. Ironically, there is even a small Plot Hole when he calls them crazy for challenging the ocean for such a silly thing - how does he even know that they came from the other side of the world when it's the first time he sees Iberians and he doesn't even know that people pay a lot for especería just some islands away?
Warfare
In real life, the Portuguese Empire did send ships to try to destroy Magellan's fleet, but the latter evaded all of them throughout a mix of luck and skill. In the series, a Portuguese fleet reaches them in the Canarian Islands and either captures or destroys the Santiago, which in real life was shipwrecked much later, after all of the five ship had artived unharmed in the South American coast. It's also notable that the Portuguese fleet is improbably large, being apparently composed by a dozen of ships of the line, which in real life would be bigger than the average of the armadas da Índia Portugal sent across their empire every year.
The clothing and armor used in the series is downright bizarre, with unnatural amounts of leather, metal studs, big kneeboots and weird armored garments left and right, often looking straight out of a Folk Metal festival rather than 16th century Spain. The most blatant examples may be Elcano's armored waistcoat and Omar's gladiator-like suspenders.
Magellan has two of the mutineers shot with arquebuses. In real life, considering gunpoweder was a precious resource in all expeditions and fleets, this would have been the equivalent of a modern army executing deserters by blowing them up with a tank cannon.
Characters
Álvaro Morte claims to have done a lot of research that shows that, despite appearances, Elcano wasn't really a devout Catholic, and this is how he portrays the character. This might be the most controversial license, as pretty much all evidence is that Elcano was, in fact, a devout believer, who participated in a mass in front of the Virgen de la Victoria of Seville to ask for luck in the travel, and whose very first act after managing to return alive to Seville was going to the same church to thank the Virgin Mary. The nuance of portraying Elcano as a Lovable Rogue, or rather a drunkard and whoremonger, is also inaccurate, as sources imply rather he was kind of a serious, introverted man without any reputation of this kind.
Magellan is given a seizable hero upgrade in this portrayal, as it either excises or excuses his most unsympathetic moments. In real life, there is an agreement that, while a great navigator, Magellan was a petty, brutal man and an unskilled leader, who demanded total obedience from his crew and often arrested people by the least grievances.
In real life, Elcano was the bosun of the Concepción, not the pilot, who was João Lopes Carvalho. Elcano wasn't reputed to have any special skill as a pilot or anything else and wasn't recruited for this reason (and certainly not from prison).
By portraying him as a langorous, apathetic boy surrounded by a veritable army of red chasubles, the series strongly implies that the young Charles V was a Puppet King in the hands of his Cardinals and associate churchmen, which was certainly not the case in real life.
In real life, Antonio de Pigafetta wasn't a complete Fish out of Water as in the series, as he had plenty of experience in travels and warfare when he joined the expedition.
There is a free black crewmember in the series, which might have been definitely possible for the time and place, but which no chronicle registers.
Gaspar de Quesada was not only beheaded as in the series. On Magellan's orders, the crewmembers cut his corpse in pieces and impaled those as a warning.
Elcano wasn't Magellan's immediate sucessor in real life. That was João Lopes Carvalho again, who was demoted for being a jerkass.
In the series, Magellan's wife and son, Beatriz Barbosa and Rodrigo Magallanes, are alive when Elcano returns to Spain, when in real life they were both long dead.
Events
In real life, King Charles V wasn't personally present in Seville to watch the expediton sail off, as he was in Barcelona at the time. Similarly, the previous meeting between Magellan and him took place in Valladolid, not Seville.
In real life, Magellan and Elcano weren't aboard of the same ship. The former was in command on the Trinidad, and the latter served in the Concepción.
Cartagena's mutiny in the series is motivated mainly by personal jealously and jingoistic mistrust towards a non-Spaniard, while in real life there were much stronger reasons, namely that Magellan was a reserved, authoritarian commander who changed his plans on the fly without explanation and refused to consult his decisions with Cartagena as he was supposed to do, which caused him to be seen as incompetent and a despot by the officers
In the series, the San Antonio vanishes without a trace in a storm through the Magellan Strait. Rather than being taken over by another mutiny, the implication given in the series is that it sank in the storm.
In the series, Lapulapu attacks first and actually threatens Magellan on his face before the Battle of Mactan, while in real life Magellan ordered the attack on Mactan as a show of power.
The Battle of Mactan itself is reproduced rather faithfully to the chronicles, but it has Magellan dying gently from an arrow to the neck before being double-tapped by a crowd of natives with spears, while in real life he only fell over due to his leg wound and was killed by them at that moment.
Humabon's betrayal didn't involve attacking the Spaniards in a meeting in his throne room, but during a feast.
The series claims none of the Trinidad's crewmen returned to Europe, but in real life, at least five of them did, among them its very captain, Gonzalo Gómez de Espinosa.
Most egregiously, the series claims at its conclusion that the route discovered by Magellan was the key for Spain to dominate the Pacific spice trade. This is completely false, as the route in question was deemed too long and arduous to be of any commercial interest. The true keys were the previous discovery of the Pacific Ocean by Vasco Núñez de Balboa and the posterior Conquest of the Aztec Empire by Hernán Cortés, which allowed the Spanish Empire to spread an infinitely easier route from Spain to México and from México to the Pacific. In fact, this was exactly the course followed by the fleet headed by Miguel López de Legazpi that achieved the Conquest of the Philippines. Magellan's route was certainly relevant to the cosmography of the time due to all the geographic knowledge it brought, not to mention for the supplying of future Spanish properties on modern day Uruguay and Argentina, but as a trade route it was simply not practical enough.
