If you are a UK based account holder, you don't have to enter your PIN for payments of £100 and under. However, you will be prompted to enter your PIN when the cumulative amount spent reaches £300.
If you are an EU based account holder, your contactless limit is €50 (or equivalent in other currencies). You will be asked to enter your PIN when the cumulative amount spent reaches €150 (or equivalent in other currencies).
If you have just received your new sync. card, please remember to activate Contactless by making a Chip & PIN payment first.