In the server section of the config, pertaining to villager gifting, the description of the customizable list is as follows:

The names of the items/blocks that can be gifted in addition to the default items. Include hearts value preceded by |.

Default (but disabled by commenting?) values are:

    #fermented_spider_eye|25
    #poisonous_potato|12

I looked everywhere for some sort of explanation as to the "hearts value". Most people would assume "1 heart value = 1 heart". Default entries of 25 and 12 suggest otherwise. Eventually I found a post on the forum from about a year ago where you commented on a post that 10 "heart points" = 1 "heart".

I suggest adding that information to the villager gifting description. Perhaps:

The names of the items/blocks that can be gifted in addition to the default items. Include heart-points (10 points = 1 Heart) value preceded by |.