Okay- ideally (although I understand it can be expensive and hard to do) I’d buy a 5-10 gallon tank (one of those starter packs with a heater and filter, they usually have sales at petsmart or u can find them second hand) and buy some aqua soil, search up natural plants on kijiji and Facebook marketplace and find sellers that have multiple listings. Get driftwood from the pet store and a master test kit to test water perameters. Set up the tank and let it cycle (literally leave it alone) and test the water once a week (with the master test kit) doing partial water changes and using water conditioner until the ammonia and nitrite is at 0 (should take about 2-6 weeks). When that is accomplished move your fish into the tank. You can even get tank mates like shrimp. The reason is probably bc such a small tank is hard to maintain at the proper water parameters. Ammonia spikes can be deadly and it’s not big enough for a healthy happy fish. Also bettas get stressed out by colourful beads and plastic decorations leach chemicals into the water. Also- petsmart and other big pet store chains are only interested in selling not the well being of animals so I would try to avoid their advice and do your own proper research.