I know you can check your balance online, but don't think you can make payments through the Agricredit web site. As mentioned above my credit union offers electronic bill pay, which is how I do it.
Mahindra (2011)5035 HST TLB & (2016)2555 HST Cab & (2017)1526 HST(2018)Cub Cadet Pro Z 154L (1991) Caterpillar E70B
I also have my payments thru automatic electronic transfers directly from one of my bank accounts. Works great for me. These days, the only bill I pay thru the post office is the credit card.