I can’t find this source again(, when they said that they lacked time to send observers), it wasn’t talked much at the time, but i’m positive it happened, here’s an example of refusal for 2020 though : theglobeandmail.com/…/article-eu-says-it-wont-sen…
Apparently, they’ve agreed to send observers in 2021 : postguam.com/…/article_8df8438a-50d1-11ec-b8be-13…
The last time was in 2015, once again at the request of the venezuelan government : www.eeas.europa.eu/node/26227_en
Some people say that the government won’t ask again in 2024 : reuters.com/…/venezuela-will-not-allow-eu-electio…
But i’ve clearly overestimated the impact : Venezuela will still be sanctioned and the public opinion will still consider that they’re miscounting the votes. Allowing international observers or not doesn’t change anything in the end, we’ll only be satisfied once the socialist revolution is out, and will continue to accept unsatisfying electoral conditions with our allies(, e.g., in Africa).
You’ll need to read pro-venezuelans medias to see the other point of view.