Some pieces are definitely connected and cannot be placed separately. Try to identify them.

Those pieces are 0 and either 1 or 7.

These pieces have another feature that limits the number of possible positions they can occupy.

One side of each of these pieces is perfectly straight. That straight edge must always be placed along the border of the frame.Only numbers with a triangular notch can be placed in the middle of the puzzle, because that notch allows the tip of another number to fit into it.

The number 7 fits inside the 0.

The numbers 2, 5, 6, and 9 are fairly interchangeable. If you get stuck, try swapping one of them for another—for example, replace 2 with 6 or 5 with 9—and see if that leads to a solution.

The 0 and 7 are placed along one of the shorter sides of the frame, occupying exactly half of its length, with the 7 facing toward the longer side of the rectangle.

From here, it's all about systematic trial and error. Build a decision tree of possible arrangements, be patient, and you'll find the solution :)