As a general rule, real estate agents are reluctant to accept cash as this creates a security risk. The choice of methods to pay your rent usually includes direct debit, money orders and electronic funds transfer.
The most important thing to do is to contact the agent (or the owner if you are not renting through an agent) as soon as you are aware there will be a problem with your rent payment. Simply ignoring the problem will not make it go away and will very likely cause the agent or the owner to become concerned and commence breach and/or eviction proceedings.
If your inability to pay the rent is only a temporary matter, you and the agent or owner may be able to come to a mutually convenient payment plan to assist you bring your rental up to date.
Be aware that you may continue to receive breach notices while your rent is in arrears but your agent or owner may agree to void these once your rental is up to date. Again, we stress the importance of communication. Let the agent or the owner know what is going on, particularly in regards to any further changes to your circumstances.