SAP router strings are case-insensitive, which means that uppercase and lowercase letters are treated the same way. Therefore, it doesn’t matter whether you use uppercase or lowercase letters in your SAP router string. However, it’s a common convention to use uppercase letters for the SAP router string, as this makes it easier to read and identify. Additionally, some older versions of the SAP router may not recognize lowercase letters in the string, so it’s best to stick to uppercase letters to avoid any potential issues.