@Annamaria1923
Your first two entries cancel each other out, and the last two are the same as creating a monthly invoice and then receiving payment on that invoice.
To reiterate, it's improper lease accounting to recognize the full $6,000 contract amount on your balance sheet if this is an operating lease (presumably it is). Just create the $600 yearly invoice and receive payment on it.
From PWC (link here):
If a lease is classified as operating, the lessor should keep the asset underlying the lease on its balance sheet and continue to depreciate the asset based on its estimated useful life. Rental revenue from lease payments should be recognized on a straight-line basis (or another systematic basis if that basis is more representative of the pattern in which income is earned from the underlying asset over the term of the respective lease).