Most states require a fee-free payment option to be available by law, and you absolutely can mail a check to their business address to pay your rent. Send it via registered mail and retain the receipt, the company cannot claim that rent was unpaid or they didn’t receive it because you then have proof of payment that is valid in all 50 states.

Mandatory fees not disclosed in the lease are an open and shut small claims court case in all 50 states in the US, with the property management company themselves paying your filing costs in addition to the amount they’ve illegally charged in fees (with some states tacking on additional punitive damages for good measure).

That said they’re allowed to charge fees for various “convenient” forms of payment. Mailed or hand-delivered cash or check are always fee-free unless otherwise specified in the lease (and fee-free regardless of what the lease says in most states which require at least one fee-free option to pay rent).