How to enable Virtual Server in BIG-IP?

Simply add automap to the VIP to exclude it as an issue:

https://support.f5.com/csp/article/K7336

https://support.f5.com/csp/article/K7820

Because you are new to F5 I may recommmend to take getting started with BIG-IP and LTM (chec the f5 site for free and payed trainning https://account.f5.com/learnf5 ):

https://www.f5.com/services/training/free-training-courses/getting-started-with-big-ip

https://www.f5.com/services/training/free-training-courses/getting-started-with-big-ip-local-traffic-manager-ltm

CBT has an old but nice trainning for F5 where you are trained how to create a virtual f5 lab on vmware:

https://www.cbtnuggets.com/it-training/f5

And finally the operations guides that are around 100 pages but a great thing:

https://support.f5.com/csp/article/K73819494

For the SNAT you will see how it is set in the getting started series but for example if the VIP is SSL and you added HTTP profile without doing a decryption you will also break it or your pool members are down or faulty but you have bad health monitor to detect this etc. . For F5 HTTP/SSL/TCP issues and doing tcpdump that also logs TCP RST if the F5 is one droping the traffic after you have read the getting started to get the basic idea you may check:

https://devcentral.f5.com/s/feed/0D51T00008aVVptSAG