Most Japanese plums require a second variety for cross pollination. And because they are early bloomers, they are often not recommended for areas that can experience late spring frosts that will affect the flowering. Without knowing the variety you are growing, either of these could be reason for lack of flowering and fruiting.

Cannot comment on any need for pruning without seeing the tree. Any chance of photos?

Prunus salicina beauty. Dwarf beauty Japanese plum.

We were told that cross pollination was not required for this variety. In fact that's why we bought it.

As it is a self fertile variety, then maybe it was the flowers that were damaged by a late frost.....this selection can bloom very early!! And you would need to have active pollinators working the area when the tree was in bloom......was that the case?

It's possible that there was a late frost. Not uncommon here. But what was concerning for me was that it didn't produce many flowers to start so it's not as if it produced hundreds and they were affected by frost and fell off. Unless the frost affected buds before they ruptured. As for pollinators I remember the year before the tree was covered in flowers and pollinators were swarming it. This past spring not so much.

Since the tree is young it probably just needed a rest for a year or it's biennial. I'd prune it in early spring, cut some branches out to get more light in and cut remaining long sprouts about a third back. Your new wood will be making fruiting spurs and flowers next year.

Speaking of fruiting spurs... do plums only grow on new growth only? or do they also grow on old wood? Will cutting back new growth to 1/3 like you said reduce future yields?