It will not be advisable to make transactions in bitcoin within a country where cryptocurrency transactions are illegal by the law. But Imagine this scenario that someone has been using their bitcoins for transaction secretly successfully, and then one day decides to use the bitcoin that they have to make payment for something like a property to the owner of the property, If there is this kind of problem for instance where the owner of the property decides to claim that they did not receive any money in bitcoin, and the case is taken to a law court, what do you think the outcome of the case will be?
If proofs of payment are provided but in cryptocurrency, do you think the court will consider it even though transactions are tagged illegal with it? or will the case be thrown out and the owner of the property with the false claim of not receiving the money be allowed to go freely?
You should never enter into a Bitcoin transaction agreement with any party in a country that does not accept Bitcoin, i.e. where it would be considered a criminal offence.
If you want to do a business deal with a party, you must do the transaction in the local currency of that country, otherwise, if the transaction is done through Bitcoin, and if a party denies the transaction, then both parties will be punished in the legal trouble.