I am building a homebrew race that will have expertise in their choice of martial weapon. I've added what I believe is the correct modifier, but it's not working on the character sheet. 

add modifier > modifier type expertise > modifier subtype choose martial weapon

I'm not sure what I'm doing wrong here. 

Link to un-published homebrew race: 

https://www.dndbeyond.com/races/385301-blackbeards-badak

Expertise does not apply to weapons/armor, spells, or languages. Only Skills and tools benefit from expertise.

Quote from IamSposta >>

Expertise does not apply to weapons/armor, spells, or languages. Only Skills and tools benefit from expertise.

 Thanks. I knew the rules didn't ever use expertise on weapon attacks, but it was an option so I figured it would work.

Do you know of a way I can grant double proficiency on attack rolls with a certain weapon or type of weapon? Besides editing the character sheet.

Not that I’m aware of, sorry.

Quote from IamSposta >>

Not that I’m aware of, sorry.

 Thanks, I'll figure out an alternative. At least I'm not chasing my tail on this any longer. 

Happy to help. Besides, a character only gains +4 proficiency bonus above starting anyway, so you’re only gonna have to adjust the attack modifiers on the sheet 4 times.