Once you’ve downloaded the plugin, head over to Ipaymu.com to sign up for an account and get your Api Key.
If you have an Api Key, you can copy and paste that on woocommerce setting > Payment gateway > ipaymu tab, paste on API Key fields. Save it.
Keep in mind, Ipaymu don’t care about your currency yet. You should set up your price on Indonesian currency, because if you set up your price $50/item, Ipaymu going to process that as Rp50/item or IDR50/item.