You cannot buy a Monthly plan when purchasing an eSIM profile with a preloaded data plan from the website as you have no Ubigi account yet. A Monthly plan requires a credit card to be registered in your Ubigi account for the payment of its monthly fee.
For the purchase of your eSIM profile with a preloaded data plan, you can choose a One-Off data plan listed on this page our website. Once you have installed your Ubigi eSIM profile and created your account, you will be able to recharge your account at anytime with One-Off plans but also Monthly plans and Annual plans.”