Can you check back with the shop (as in walk in & look
) - lampeye's can be sensitive to the shipping/wholesaler/retailer/consumer transfer chain, in general don't purchase unless they are active & "shining" in the shop tank (or if you have a quarantine tank, low light, no CO2, matched parametres etc tank to move them into)
Once established in your tank they are still somewhat CO2 sensitive - not as sensitive as the checkerboard cichlids I kept them with - but it took them a couple months to acclimate to moderate CO2; if you have a high CO2 tank, they're unlikely to thrive.
When adding new fish, I have lights off, good aeration, & don't feed for 24h, I leave the tank with lights off for this period, then introduce lighting & reduced CO2 on Day 2 of New Fish.
Depending on species, all of this (& more) may be necessary ... or none of it
I often pick up fish & shrimp direct from the shipping bags (best selection in my area) so depending on how long fish have been in transit, I may leave lights off for 3-4 days - there's sufficient ambient light for me to judge fish (shrimp) appearance/behavior.
If it's a busy community, I often use a quarantine tank, or if I don't have a suitable Q tank, will move existing stock to alternate quarters while new fish (shrimp) become established.