Card as a means of payment in Cuba.
I recently took a trip to Cuba, and the first thing I did was coordinate transport to Varadero from Havana, with the surprise that both Havana and Varadero do not accept credit or debit cards, as the signal is very bad, some shops do not have data or are damaged, no repair date.
If you want to get money out of ATMs, you have to know that the signal could also be interrupted, and you have to wait a few hours or find another ATM.
Being accustomed to paying most of the services and shops with cards, we did not think that we had to walk so effectively, in my case there was a sum of euros (because dollars are taxed at 10%), but the strange thing is that no boking review, or any page on trips to Cuba, or anyone who had travelled to Cuba, informed us about this.
So my advice is to change as many Euros as possible, don't be afraid to walk around in your wallet or wallet as Cuba is extremely safe for the tourist, and if you prefer, you can keep a piece in the hotel or accommodation safe.