Sforno on Leviticus 22:23/ספורנו על ויקרא כ״ב:כ״ג

1נדבה תעשה אותו, even though numerous blemishes may be apparent you may donate them for the Temple treasury although the donor thought that on account of these blemishes they would be rejected by the Temple treasurer. The Torah differentiates between gifts for the Temple treasury and animals destined for the altar. Whereas even minor blemishes disqualify an animal from being offered on the altar, no such restrictions apply to gifts known as נדבה. This is possible because the bodies of such animals do not possess any sanctity, such sanctity only applies to their value, i.e. to the money realised from the sale of such animals. This enables the body which was donated to be treated as if it had never been sanctified in any way.