Proof of income for a new job while apartment searching?

I hope this is the appropriate forum to post. I just got a new job, and am apartment hunting because I want to move into the city my job is located.

A lot of landlords/property management co's want to see proof of income or proof of employment, but I don't have access to this yet (besides my offer letter which lists my hourly pay). Maybe a stupid question -- can I show them my offer letter? How else can I prove income/employment before I can get other official paperwork?

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