The error occurs in two cases,
Insufficient Unassigned Value in Budget -
The value you assign to the User's Card has to be less than or at least equal to the unassigned value of the corresponding budget.
For example the "Sales Budget" has a budget goal of 1000 SGD, and already assigned value to other cards is 800 SGD. So your unassigned value will be 200 SGD. Then if you create a load more than 200 SGD it will throw an error.
Solution : In this case, Increase the budget goal to ensure the unassigned value of the budget is greater than the fund you want to load.
Insufficient Unassigned Value in the Volopay Wallet -
The value loaded to the Card has to be less than or equal to unassigned value in the Volopay Wallet, even if the Budget's unassigned value matches that of the Virtual card.
Lets take the same example the "Sales Budget" has a budget goal of 1500 SGD, and already assigned value to other cards is 800 SGD. So your unassigned value will be 700 SGD. Then if you fund a card for 200 SGD it will throw an error if the unassigned value in the main Volopay wallet has only 100 SGD unassigned value.
Solution : In this case, kindly fund you Volopay wallet to credit amount in the Volopay wallet.