[01:48:24] [Server thread/ERROR]: Couldn't load advancement simpleores:recipes/onyx_bow: Task Advancement{parentId=simpleores:recipes/onyx_tools, display=null, rewards=AdvancementRewards{experience=0, loot=[], recipes=[simpleores:onyx_bow, simpleores:onyx_rod], function=null}, criteria={has_recipe1=net.minecraft.advancements.Criterion@6e76562c, has_recipe2=net.minecraft.advancements.Criterion@1c64b9d1, has_string=net.minecraft.advancements.Criterion@4e4093f9}, requirements=[[has_string, has_recipe1, has_recipe2]]}

I get this error when starting up the server. I am not sure how to fix this, don't want to mess around in the code because I don't know what I am doing. Please help me out! Thanks.

Versions prior to 1.12.2 are no longer supported. In SimpleOres2 1.12.2-1.11.2.0, onyx bows are craftable just fine. I cannot duplicate or clearly identify a bug here. The error message you posted from an older version relates to the "hidden" advancements that add recipes to the crafting table recipe book. You can still craft stuff without that.