Gold Healing an Allies Troops

I virtually never gold heal my own troops, but I recently had a situation where I was going to for an alliance mate's troops. While attempting this, I got an error message that said "You don't have enough Goldmarks to use this premium action." I have a premium account. Not sure what else I would need. Has anyone else come across this? Hopefully I'll never be in a position to do this again, but this one has me curious.