No. After the initial funding there is no monthly obligation, no minimum ongoing contribution, and no penalty for leaving your balance untouched.
You can set up a recurring deposit if you want to save consistently, and you can pause or cancel it any time in the app. Each recurring deduction carries the payment provider's fee, so if you are contributing small amounts, depositing less frequently in larger amounts costs less in total.
There is also no maximum. You can add lump sums whenever you like.