Does EU roaming work in Bosnia and Herzegovina?

No! This is the #1 roaming trap. Although Bosnia is in Europe, it is NOT a member of the European Union (EU). Your "Roam Like at Home" (RLAH) plan does not apply. Most EU and UK carriers (like Vodafone, O2, EE, T-Mobile DE) will charge you extremely high international roaming fees (e.g., £2-£6 per day). A Ti Porto in Viaggio eSIM is the only way to get a fixed, cheap data price.