Before a call connects, SpareLine checks a few things. If one of them fails, the call is not started and nothing is charged.
The balance does not cover it
A call needs enough balance for its first few minutes. Add balance and try again. See Adding money to your balance.
Billing details are missing
Calls need billing details, because the VAT on a call is worked out from them. Add them under Account → Billing details and try again. See VAT on your purchases.
The number is busy
A number can be on one call at a time. If it is already on a call, in either direction, another one from it is not started.
SpareLine does not carry calls to that destination
SpareLine calls a destination only when it has a price for it, and it does not carry calls to some very expensive destinations. Trying again will not help. The app tells you when this is the case.
Too many calls too quickly
To protect your balance, SpareLine limits how quickly one account can start calls and how many can run at once. Wait a moment and try again. Nothing is wrong with the number, the destination or your balance.
The account is frozen
A frozen account cannot make calls, and adding balance does not change that. See My account is frozen.
Emergency numbers
SpareLine never calls emergency numbers. See Emergency calls.