Check out the rules of golf rule 15 that states that you must hole out with the exact same type of ball that you teed off that hole with.
The reason for this rule is to stop players using balls for different situations on the course, eg, hard balls for the extra distance off the tee then swapping to a super soft ball for approach shots to the green for stopping power.
The solution to this is next time you click on to play then check your equipment window and see how many balls you have left before you start a round and buy some in the pro shop to avoid having to play with starter balls in the event of losing "that 1 ball".
Cheers.