UNITED24 is the initiative of the President of Ukraine to collect donations for defence, humanitarian, medical, education and rebuilding projects. 

Björn recorded a second (I have assumed his first one was Hela Sverige skramlar för Ukraina) message of support:

"Dear Brave Ukrainians

My name is Björn Ulvaeus and this is my second message of empathy and solidarity from Stockholm, Sweden.

I don't think any of us here could have imagined that there would be a new war in Europe. I myself was born on April 25th 1945. I experienced a real feeling of threat from the Soviet Union. We were so close geographically and the Soviets seemed so powerful and invincible and could so easily have taken Sweden.  

As a young man I thought about what it would be like to live under the communist rule and I came to the conclusion that I was prepared to die to defend the freedom we had in Sweden. So I think I understand you who you are fighting, with your lives at stake to maintain freedom in Ukraine. We must help you at all cost. We, who understand how brittle and vulnerable liberal democracy can be, we must stand with you grateful that you are our champions in the fight against strong men and deliberate dictators."

United24
United24 (Björn)
United24 (Björn)

YouTube link c/o Episodes of Bushwhacking, Tales from Warzone