Problem Deploying to Testnet

Howdy y’all! So I’m working as a freelancer and I’m trying to deploy a contract to testnet so I can… you know …test it. But I keep getting this error:

Error: *** Deployment Failed ***

“Migrations” – invalid sender.

I’m using MacOS Big Sur 11.2.3, but it seems like people with both windows and mac are having this issue so not sure how helpful that info is.

I’ve been researching for a couple hours now and I can only find a few online forums dealing with this but none of their solutions seem to work for me, and some of them haven’t found solutions at all. Hoping someone here can help me out!