The smallest micro SD card I could find was an 8 Gb micro SDHC card at the dollar store. I have never bought anything smaller or lower quality than a class 10 chip. I didn't think they made micro sized SD chips with less memory. Where can a person buy one of these antique chips?
for basic hd 720p-1080p class 6 is about minimum for good results.
for 4k class 10 a v30-v90 best though v10 is minimum
when someday we get 8k then you'd need minimum v30
for reference sake a 32gb v30 name brand sd card on amazon is $18.
i never paid that much attention until i got my first drone several years back. the newest shoots at 4k. if i use anything less than a v30 card the video portion has 'issues' so to speak. sort of like expecting a 4 cylinder engine to give you bugatti performance.
It should only fit in one orientation. I think the pins face down. Make sure it clicks into place. You usually have to use your fingernail to get it to go all the way in. When it's in all the way, it will be pretty much flush with the case.