The APR (Annual Percentage Rate) corresponds to the annualized gross interest rate. This indicator is an estimate of the rewards you may earn.
The APR applies to the quantity of crypto assets in the staking contract, not to the amount invested in euros.
Example: You purchase 100 MATIC on 01/01/2023, with a 5% APR. If it remains constant throughout the year, by 01/01/2024, your investment will have generated 5 MATIC in interest.
See also: What is the difference between APR and APY?