The myTax service is only billed once per tax year (at the standard rate of €40 at launch in March 2022).
You are free to start filling in the myTax questionnaire at no charge. Only after this has been finalised and before accessing the results of the tax report and its various forms does this billing take place. You can then return to the questionnaire to generate new versions of the tax report and its various forms without additional billing.
Please note: the optional use of the tax safe is completely free of charge.