ram slots not working

I have an MSI b550 gaming plus and a single 8gb ram 3200mhz t force delta, I tried putting it on dimmb2 and dimma2 and they didn't work but when I put it in dimmb1 it worked but when I booted the pc for the first time it said Im not putting it in the right slot and I need to change it to dimmb2 or dimma2, I'm gonna get another ram next month. specs: Ryzen 5 3600 GTX 1080 (used) 600w psu t force 8gb 3200mhz MSI b550 gaming plus 1tb nvme 120gb nvme