Health checks of Private Instance in Target Groups Shows as unhealthy

Question

I created a network load balancer(internal) to point to the private servers in the VPC, as per documentation i have done the below steps:

• Configure Security Groups to allow traffic from Client IP address as well as VPC CIDR Blocks.

But after implementing the above procedure, Target Group says that the private server is unhealthy. Below is my Target Group Config:

Protocol TCP Port traffic port Healthy threshold 3 Unhealthy threshold 3 Timeout 10 Interval 30

Please assist me here