Tried to purchase FNILX in my new 401k account and it says it's "closed to new investors"

Does anyone know why I wouldn't be able to purchase this? My 401k is a Self Employed 401k through mysolo401k.net and their plan allows you to buy anything so I'm pretty sure that's not the issue.

Is there a certain waiting period Fidelity makes you go through before purchasing something like this? Just looking for any feedback from this community. Thanks!