Q: running 10.6.8 on a mac mini.  I can no longer buy with visa card on line ?

Safari in SL and Lion and Mountain Lion too have security flaws and some site just do not allow using those browsers.

Try the FireFox browser. That is still being update for SL and later.

This month Google stopped updating Chrome browser fro Mountain Lion and below.

And Firefox will soon stop supporting Snow Leopard too.

Apr. 2016 - Firefox Snow Leopard support - https://discussions.apple.com/message/30039053#30039053 - next Firefox dropping support for all OSX versions prior to Mavericks

Is there a reason you are staying on Snow Leopard which has security issues that Apple is not fixing?

Depending on the build model year and identifier of the computer in question,

there may or may not be an upgrade potential to a newer OS X version...

• How to identify Mac mini models - Apple Support

Some early model Mini (Intel hardware) could only be upgraded to Snow Leopard

10.6.8 at the latest; later models, to Lion 10.7.5, others to Mountain Lion 10.8.5;

or then to Mavericks, 10.9.5; later some to Yosemite 10.10; no earliest model Mini

could run El Capitan OS X 10.11. due to hardware limits from that era.

So what you have will define the possibilities. If the unit is too old for El Capitan 10.11

or has other hardware limits that may work better under Mountain Lion 10.8.5, should

the unit you have be capable of Lion 10.7.5 or Later. Lion and Mountain Lion are both

purchases from the online Apple Store (not via App Store.) There are other limitations.

The computer memory usually could use an upgrade to a higher capacity of RAM chip

for a later OS X to function better; & to work with later versions of applications run in it.

Since your Mini is said to be running Snow Leopard 10.6.8, then it isn't an older PPC G4

model; so identification is not as difficult looking forward from 2005 to Intel-based Macs.

The oldest Intel-based Mac Mini that can run SL OS X 10.6.8 is a intel 1-core model:

http://www.everymac.com/systems/apple/mac_mini/specs/mac_mini_cs_1.5.html

• Apple Mac Mini - All Mac Mini Technical Specs - Everymac.com:

http://www.everymac.com/systems/apple/mac_mini/index-macmini.html

In any event...

Good luck & happy computing!

Note that if you update many apps will not work:

https://discussions.apple.com/docs/DOC-6271